Changed `NK_WINDOW_BACKGROUND` behavior
Changed `NK_WINDOW_BACKGROUND` behavior

Background windows now get only selected by hovering if no other window
is above it and not on clicks.

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