Made it easier to change header image

web/dart/reorganize_html.dart

@@ -2,13 +2,14 @@ import 'dart:html';
 
 import './navbar.dart' show makeNavbar;
 
+final image_header = 'https://cdn.phundrak.com/img/mahakala-monochrome.png';
+
 Future<Element> makeHeader() async {
   var header = Element.tag('header');
   header
     ..append(Element.img()
-      ..attributes['src'] =
-          'https://cdn.phundrak.com/img/mahakala-monochrome.png'
-      ..attributes['alt'] = 'Logo de Phundrak'
+      ..attributes['src'] = image_header
+      ..attributes['alt'] = 'Logo'
       ..attributes['heigh'] = '150px'
       ..attributes['width'] = '150px')
     ..append(querySelector('h1'));