Add an option to the menu that allows to hide/show all panels at once.
completed by: Daniel Lanzi
mentors: Torsten Rahn, Dennis Nienhüser, Utku Aydın, Andrei Dorian Duma
In the most recent version Marble has got a menu entry Settings-> Panel which lists all possible panels and allows to switch them on/off individually. This feature is supposed to stay. But in addition it should be possible to hide / show all panels altogether. This task is about finding a nice solution that allows for this addition. The solution should be implemented and submitted to review board.
Add support for a hotkey (F9) that allows to toggle between both states.