Emit an event when a local-echo is turned into a proper event

We need to trigger an update of the timeline when this happens, so raise an
event for it.

lib/sync.js

@@ -86,7 +86,9 @@ SyncApi.prototype.createRoom = function(roomId) {
     });
     reEmit(client, room, ["Room.name", "Room.timeline", "Room.redaction",
                           "Room.receipt", "Room.tags",
-                          "Room.timelineReset"]);
+                          "Room.timelineReset",
+                          "Room.localEchoUpdated",
+                         ]);
     this._registerStateListeners(room);
     return room;
 };