Allow untiling windows with the same shortcut as used for tiling

Submitted by Andrzej

Assigned to Olivier Fourdan @olivier

Link to original bug (#8768)

Description

Currently windows can by untiled by pressing unmaximize button or using maximize window shortcut key.

This feels a bit awkward in practice. It would be much more convenient if the window could be untiled/unmaximized by pressing the same tile shortcut key again.