[Emacs] Remove unused code, reorganize file, add configuration

Removed the head variable for `org-confirm-babel-evaluate' since I set
it to `nil' anyway.

Add `:mkdir yes' to all `:tangle' header arguments so no issues arise
when trying to tangle.

Added three new packages:
- helm-icons for integrating all-the-icons in Helm
- org-tree-slide for orgmode powered presentations
- wrap-region for wrapping selections with other chars than
  parenthesis

Renamed variables in my custom Elisp functions so they stand out more
as user-defined variables.

Renamed `shortcuts' to `keybindings'

Added keybindings for `org-tree-slide'

Updated dotspacemacs file

.spacemacs

@@ -121,7 +121,7 @@ This function is called at the very end of Spacemacs initialization."
  '(objed-cursor-color "#ff6c6b")
  '(org-export-headline-levels 4)
  '(package-selected-packages
-   '(org-treeusage caddyfile-mode org-ref lsp-dart mu4e-maildirs-extension mu4e-alert helm-mu xkcd vmd-mode visual-fill-column typit mmt sudoku restclient-helm pony-mode pacmacs ox-reveal outorg ob-restclient ob-http meson-mode ibuffer-projectile lv helm-w3m w3m graphviz-dot-mode flycheck-gometalinter transient ess-smart-equals ess-R-data-view ctable ess julia-mode eshell-git-prompt emoji-cheat-sheet-plus edit-indirect dockerfile-mode docker docker-tramp company-restclient restclient know-your-http-well company-quickhelp company-emoji company-emacs-eclim eclim atomic-chrome websocket 2048-game ox-gfm slime-company slime common-lisp-snippets erlang insert-shebang fish-mode company-shell faceup racket-mode treepy graphql yapfify yaml-mode xterm-color web-beautify twittering-mode toml-mode tagedit stickyfunc-enhance smeargle slim-mode shell-pop selectric-mode scss-mode sass-mode ranger rainbow-identifiers pytest pyenv-mode py-isort pug-mode plantuml-mode phpunit phpcbf php-auto-yasnippets pdf-tools tablist ox-pandoc orgit org-present org-pomodoro alert log4e gntp ob-elixir multi-term markdown-toc magit-gitflow magit-gh-pulls livid-mode live-py-mode json-snatcher js2-refactor js-doc htmlize hlint-refactor hindent helm-pydoc helm-hoogle helm-gitignore helm-css-scss haskell-snippets haml-mode gnuplot glsl-mode gitignore-mode github-search github-clone github-browse-file gitconfig-mode gitattributes-mode git-messenger gist gh marshal logito pcache ht gh-md flyspell-correct-helm flyspell-correct flycheck-rust pos-tip flycheck-mix flycheck-credo eshell-z eshell-prompt-extras esh-help drupal-mode disaster cython-mode dash-functional tern company-ghci company-ghc ghc color-identifiers-mode cmm-mode clang-format cargo auto-dictionary alchemist modern-cpp-font-lock yasnippet-snippets x86-lookup web-mode srefactor racer pyvenv pip-requirements pandoc-mode org-projectile org-category-capture org-mime org-download nasm-mode json-reformat intero imenu-list hy-mode git-timemachine git-link geiser flycheck-pos-tip flycheck-haskell evil-magit emmet-mode cmake-mode anaconda-mode rust-mode elixir-mode flycheck haskell-mode multiple-cursors skewer-mode simple-httpd markdown-mode magit magit-popup git-commit ghub with-editor pythonic emms gmail-message-mode ham-mode html-to-markdown flymd edit-server image-dired+ go-guru go-eldoc company-go go-mode unfill mwim company-web web-completion-data company-tern company-cabal company-c-headers company-auctex company-anaconda elcord xresources-theme sql-indent rainbow-mode php-extras php-mode mmm-mode json-mode js2-mode csv-mode coffee-mode auctex helm-company helm-c-yasnippet fuzzy company-statistics company auto-yasnippet yasnippet ac-ispell auto-complete ws-butler winum which-key volatile-highlights vi-tilde-fringe uuidgen use-package toc-org spaceline powerline restart-emacs request rainbow-delimiters popwin persp-mode pcre2el paradox spinner org-plus-contrib org-bullets open-junk-file neotree move-text macrostep lorem-ipsum linum-relative link-hint indent-guide hydra hungry-delete hl-todo highlight-parentheses highlight-numbers parent-mode highlight-indentation helm-themes helm-swoop helm-projectile helm-mode-manager helm-make projectile pkg-info epl helm-flx helm-descbinds helm-ag google-translate golden-ratio flx-ido flx fill-column-indicator fancy-battery eyebrowse expand-region exec-path-from-shell evil-visualstar evil-visual-mark-mode evil-unimpaired evil-tutor evil-surround evil-search-highlight-persist evil-numbers evil-nerd-commenter evil-mc evil-matchit evil-lisp-state smartparens evil-indent-plus evil-iedit-state iedit evil-exchange evil-escape evil-ediff evil-args evil-anzu anzu evil goto-chg undo-tree eval-sexp-fu highlight elisp-slime-nav dumb-jump f dash s diminish define-word column-enforce-mode clean-aindent-mode bind-map bind-key auto-highlight-symbol auto-compile packed aggressive-indent adaptive-wrap ace-window ace-link ace-jump-helm-line helm avy helm-core popup async))
+   '(curl-to-elisp org-tree-slide wrap-region helm-icons org-treeusage caddyfile-mode org-ref lsp-dart mu4e-maildirs-extension mu4e-alert helm-mu xkcd vmd-mode visual-fill-column typit mmt sudoku restclient-helm pony-mode pacmacs ox-reveal outorg ob-restclient ob-http meson-mode ibuffer-projectile lv helm-w3m w3m graphviz-dot-mode flycheck-gometalinter transient ess-smart-equals ess-R-data-view ctable ess julia-mode eshell-git-prompt emoji-cheat-sheet-plus edit-indirect dockerfile-mode docker docker-tramp company-restclient restclient know-your-http-well company-quickhelp company-emoji company-emacs-eclim eclim atomic-chrome websocket 2048-game ox-gfm slime-company slime common-lisp-snippets erlang insert-shebang fish-mode company-shell faceup racket-mode treepy graphql yapfify yaml-mode xterm-color web-beautify twittering-mode toml-mode tagedit stickyfunc-enhance smeargle slim-mode shell-pop selectric-mode scss-mode sass-mode ranger rainbow-identifiers pytest pyenv-mode py-isort pug-mode plantuml-mode phpunit phpcbf php-auto-yasnippets pdf-tools tablist ox-pandoc orgit org-present org-pomodoro alert log4e gntp ob-elixir multi-term markdown-toc magit-gitflow magit-gh-pulls livid-mode live-py-mode json-snatcher js2-refactor js-doc htmlize hlint-refactor hindent helm-pydoc helm-hoogle helm-gitignore helm-css-scss haskell-snippets haml-mode gnuplot glsl-mode gitignore-mode github-search github-clone github-browse-file gitconfig-mode gitattributes-mode git-messenger gist gh marshal logito pcache ht gh-md flyspell-correct-helm flyspell-correct flycheck-rust pos-tip flycheck-mix flycheck-credo eshell-z eshell-prompt-extras esh-help drupal-mode disaster cython-mode dash-functional tern company-ghci company-ghc ghc color-identifiers-mode cmm-mode clang-format cargo auto-dictionary alchemist modern-cpp-font-lock yasnippet-snippets x86-lookup web-mode srefactor racer pyvenv pip-requirements pandoc-mode org-projectile org-category-capture org-mime org-download nasm-mode json-reformat intero imenu-list hy-mode git-timemachine git-link geiser flycheck-pos-tip flycheck-haskell evil-magit emmet-mode cmake-mode anaconda-mode rust-mode elixir-mode flycheck haskell-mode multiple-cursors skewer-mode simple-httpd markdown-mode magit magit-popup git-commit ghub with-editor pythonic emms gmail-message-mode ham-mode html-to-markdown flymd edit-server image-dired+ go-guru go-eldoc company-go go-mode unfill mwim company-web web-completion-data company-tern company-cabal company-c-headers company-auctex company-anaconda elcord xresources-theme sql-indent rainbow-mode php-extras php-mode mmm-mode json-mode js2-mode csv-mode coffee-mode auctex helm-company helm-c-yasnippet fuzzy company-statistics company auto-yasnippet yasnippet ac-ispell auto-complete ws-butler winum which-key volatile-highlights vi-tilde-fringe uuidgen use-package toc-org spaceline powerline restart-emacs request rainbow-delimiters popwin persp-mode pcre2el paradox spinner org-plus-contrib org-bullets open-junk-file neotree move-text macrostep lorem-ipsum linum-relative link-hint indent-guide hydra hungry-delete hl-todo highlight-parentheses highlight-numbers parent-mode highlight-indentation helm-themes helm-swoop helm-projectile helm-mode-manager helm-make projectile pkg-info epl helm-flx helm-descbinds helm-ag google-translate golden-ratio flx-ido flx fill-column-indicator fancy-battery eyebrowse expand-region exec-path-from-shell evil-visualstar evil-visual-mark-mode evil-unimpaired evil-tutor evil-surround evil-search-highlight-persist evil-numbers evil-nerd-commenter evil-mc evil-matchit evil-lisp-state smartparens evil-indent-plus evil-iedit-state iedit evil-exchange evil-escape evil-ediff evil-args evil-anzu anzu evil goto-chg undo-tree eval-sexp-fu highlight elisp-slime-nav dumb-jump f dash s diminish define-word column-enforce-mode clean-aindent-mode bind-map bind-key auto-highlight-symbol auto-compile packed aggressive-indent adaptive-wrap ace-window ace-link ace-jump-helm-line helm avy helm-core popup async))
  '(pdf-view-midnight-colors '("#655370" . "#fbf8ef"))
  '(safe-local-variable-values
    '((org-confirm-babel-evaluate)