Improve zeroing of RoomList notification badges

Use an action and force an update when zeroing the number of notifications in a room. This is better than waiting for a `render` to happen at some point. This will hopefully fix https://github.com/vector-im/riot-web/issues/3257

src/components/views/rooms/RoomList.js

@@ -96,6 +96,12 @@ module.exports = React.createClass({
                     });
                 }
                 break;
+            case 'on_room_read':
+                payload.room.setUnreadNotificationCount('total', 0);
+                payload.room.setUnreadNotificationCount('highlight', 0);
+                // Force an update because this state is too deep to cause an update
+                this.forceUpdate();
+                break;
         }
     },