PianoRoll: CSS stylability, mousewheel improvements

Most parts of piano roll are now stylable:
- background color
- note color
- bar color (for volume bars)
- grid color
- color of the note volume/note panning text 

Some are still unstylable: selection colour, pitch/scale highlight colours. I think the selection colour would be best if it could be defined globally in one property, but I don't yet know how to go about implementing this...

addendum: mousewheel
- ctrl+alt+wheel changes q (as in auto)
- ctrl+shift+wheel changes note length
- changed note lock functionality slightly, it no longer changes itself to 1/16 because this would cause annoying infinite scrolling with the wheel, instead it just acts like 1/16 when notelength is last note