Differentiate between closing and hiding a window
Differentiate between closing and hiding a window

There is now a difference between hiding a window with
`nk_window_show` and closing a window by clicking the close button in
the window header or calling `nk_window_close`. Only in the case of
activly closing a window will be removed at the end of the frame
besides getting removed if not updated inside the frame.

OpenMusicKontrollers/moony.lv2,OpenMusicKontrollers/sherlock.lv2,OpenMusicKontrollers/sherlock.lv2,OpenMusicKontrollers/synthpod,OpenMusicKontrollers/moony.lv2,OpenMusicKontrollers/moony.lv2,OpenMusicKontrollers/moony.lv2,OpenMusicKontrollers/synthpod,OpenMusicKontrollers/sherlock.lv2,OpenMusicKontrollers/patchmatrix,OpenMusicKontrollers/synthpod,OpenMusicKontrollers/synthpod,OpenMusicKontrollers/patchmatrix,OpenMusicKontrollers/midi_matrix.lv2,OpenMusicKontrollers/patchmatrix,OpenMusicKontrollers/sherlock.lv2,OpenMusicKontrollers/midi_matrix.lv2,OpenMusicKontrollers/midi_matrix.lv2,OpenMusicKontrollers/patchmatrix,OpenMusicKontrollers/synthpod,OpenMusicKontrollers/moony.lv2,OpenMusicKontrollers/midi_matrix.lv2,OpenMusicKontrollers/moony.lv2