AutomationEditor: improve zoom, CSS

- entire wheelevent code was written very... weirdly, I simplified it
- fix bug with x zoom with mousewheel, no more getting stuck between 25/50
- ctrl+shift+mousewheel now zooms y-axis
- ctrl+alt+mousewheel now changes quantization

Addendum: CSS stylability
- background
- sidebar background and text
- grid colour
- graph colour
- vertex points colour