MELS: membership events are collapsable. Collapse them by default

Riot/Model/Room/RoomDataSource.m

@@ -130,6 +130,12 @@
     // Finalize cell view customization here
     if ([cell isKindOfClass:MXKRoomBubbleTableViewCell.class])
     {
+        // Nothing to do for collapsed cells
+        if (roomBubbleCellData.collapsed)
+        {
+            return cell;
+        }
+
         MXKRoomBubbleTableViewCell *bubbleCell = (MXKRoomBubbleTableViewCell*)cell;
         RoomBubbleCellData *cellData = (RoomBubbleCellData*)bubbleCell.bubbleData;
         NSArray *bubbleComponents = cellData.bubbleComponents;