Update UI to match https://gitlab.gnome.org/Teams/Design/settings-mockups/-/blob/master/wacom/wacom-settings.png better. Some exceptions/caveats:
- Button mapping is notoriously missing from the mockup, this is still delegated on GNOME Shell's pad OSD.
- Mockups were missing an action to calibrate the tablet, I added one where I saw fit.
- Added an "Automatic" option to display mapping, this ATM has to be separated to let GNOME Shell apply its heuristics.
- I quite made up the tablet/stylus descriptions
- Focus ring on stylus proximity is not implemented
- Monitor number OSDs is not implemented either
- Tip/eraser pressure sliders are silently still divided in 6 steps, even though they look continuous