maintain the global notification timeline set.

* track notifTimelineSet on MatrixClient
* stop Rooms from tracking notifTimelineSet as they don't need to
* Implement client.paginateNotifTimelineSet
* make Events store their pushActions properly
* insert live notifs directly into the notifTimelineSet in /sync, ordering by origin_server_ts.

lib/models/event-timeline.js

@@ -100,6 +100,14 @@ EventTimeline.prototype.getFilter = function() {
     return this._eventTimelineSet.getFilter();
 };
 
+/**
+ * Get the timelineSet for this timeline
+ * @return {EventTimelineSet} timelineSet
+ */
+EventTimeline.prototype.getTimelineSet = function() {
+    return this._eventTimelineSet;
+};
+
 /**
  * Get the base index.
  *