disconection message should not be a windows

Created by: mbonani

When user unplug a Thymio it generate a windows that tell people to reconnect the robot and freezing the back windows. If they close it they cannot reconect without restarting aseba. We propose instead of a windows to add a banner that the robot was disconected and that aseba studio is trying to reconnect, without the possibility to stop that. People could then continue to use the main windows for example saving their code. The same should be implement ins VPL standalone