Order the roomEvents models from newest to oldest

Qt somehow handles scrolling on new messages on its own when the
ListView direction is bottom to top.
In normal top to bottom, manual scrolling is completly buggy.

harmonyqml/backend/signal_manager.py

@@ -96,19 +96,17 @@ class SignalManager(QObject):
         date_time = QDateTime.fromMSecsSinceEpoch(edict["server_timestamp"])
         new_event = RoomEvent(type=etype, date_time=date_time, dict=edict)
 
-        # Insert event in model at the right position, based on timestamps
-        # to keep them sorted by date of arrival.
-        # Iterate in reverse, since a new event is more likely to be appended,
-        # but events can arrive out of order.
-        if not model or model[-1].date_time < new_event.date_time:
+        # Model is sorted from newest to oldest message
+        insert_at = None
+        for i, event in enumerate(model):
+            if new_event.date_time > event.date_time:
+                insert_at = i
+                break
+
+        if insert_at is None:
             model.append(new_event)
         else:
-            for i, event in enumerate(reversed(model)):
-                if event.date_time < new_event.date_time:
-                    model.insert(-i, new_event)
-                    break
-            else:
-                model.insert(0, new_event)
+            model.insert(insert_at, new_event)
 
 
     def onRoomTypingUsersUpdated(