added themeLoaded event

added 'themeLoaded' event that is dispatched right after a theme is loaded.

it can be used like this :
this.editor.renderer.on('themeLoaded',function(){
    //do something when the theme is loaded
});

lib/ace/virtual_renderer.js

@@ -1329,6 +1329,8 @@ var VirtualRenderer = function(container, theme) {
                 _self.$size.width = 0;
                 _self.onResize();
             }
+            
+            _self._dispatchEvent('themeLoaded');
         }
     };