UI widgets: support event-based notifications

Triggering 'cloudStack.addNotification' adds a new UI notification, to
avoid having to specify DOM element containing the jQuery widget every
time. This event accepts same args as .notifications('add', ...)

Example:

$(window).trigger('cloudStack.addNotification', {
  desc: 'Description',
  interval: 1000,
  poll: function(args) {
    ...
    args.complete();
  }
});

ui/scripts/ui/widgets/notifications.js

@@ -230,7 +230,11 @@
     return this;
   };
 
-  // Events
+  // Setup notification listener -- accepts same args as
+  $(window).bind('cloudStack.addNotification', function(event, data) {
+    $('.notifications').notifications('add', data);
+  });
+
   $(document).click(function(event) {
     var $target = $(event.target);
     var $attachTo, $popup;