## Add new fullscreen mode

Add a new fullscreen mode showing only the current active view in fullscreen (shortcut: Ctrl + F11).

The current fullscreen mode sets the tabbed multi-view widget fullscreen, i.e. all views are maximized, including
separators and decoration. The new mode is intended to be closer to a "classical" fullscreen mode.

This is in part motivated by the need of some hardware (like the zSpace Inspire) to have a strict fullscreen mode
in order to display the rendered scene correctly.
