Loading bar: Introduced two event listeners on window 'pillar:workStart' and 'pillar:workStop' that (de)activates the loading bar.

Reason:
* To decouple code
* Have the loading bar active until whole page stopped working
* Have local loading info

Usage:
$.('.myClass')
   .on('pillar:workStart', function(){
    ... do stuff locally while loading ...
    })
   .on('pillar:workStop', function(){
   ... stop do stuff locally while loading ...
   })

$.('.myClass .mySubClass').trigger('pillar:workStart')
... do stuff ...
$.('.myClass .mySubClass').trigger('pillar:workStop')

src/scripts/tagged_assets.js

@@ -25,7 +25,7 @@
         if (!node.picture) {
             warnNoPicture();
         } else {
-            loadingBarShow();
+            $(window).trigger('pillar:workStart');
 
             // TODO: show 'loading' thingy
             $.get('/api/files/' + node.picture)
@@ -34,7 +34,6 @@
                     console.log(msg);
                 })
                 .done(function(resp) {
-                    loadingBarHide();
 
                     // Render the picture if it has the proper size.
                     var show_variation = null;
@@ -57,6 +56,9 @@
                         .attr('width', variation.width)
                         .attr('height', variation.height);
                     thumbnail_container.append(img);
+                })
+                .always(function(){
+                    $(window).trigger('pillar:workStop');
                 });
         }