Added general scrollbar shortcuts
Added general scrollbar shortcuts

This commit extends nuklears scrollbar with some basic shortcuts.
Included are page up/down as well as jump to beginning and
end of window. The last scrollbar change is page down/up by mouse
click in empty scrollbar space.

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