calendar: Refresh calendar when ignored events changes

The last patch fixed marking days in the calendar where all
events are ignored, but it doesn't pick up the change when
an event is hidden. Emit an appropriate change notification
to fix this issue.

https://bugzilla.gnome.org/show_bug.cgi?id=768538

js/ui/calendar.js

@@ -311,9 +311,13 @@ const DBusEventSource = new Lang.Class({
     },
 
     ignoreEvent: function(event) {
+        if (this._ignoredEvents.get(event.id))
+            return;
+
         this._ignoredEvents.set(event.id, true);
         let savedState = new GLib.Variant('as', [...this._ignoredEvents.keys()]);
         global.set_persistent_state('ignored_events', savedState);
+        this.emit('changed');
     },
 
     requestRange: function(begin, end) {