- Changed canvas rotation reset method (was hard to trigger with a tablet pen).
- Default angle steps increased to 15 degrees.
- HUD now appear only in active viewport as it should

- Added operators to store/restore camera rotation (handy to quickly get back to a prefered angle)
- Use a modifier key to step the rotation by a user-chosen angle
- Addon preferences UI cleanup

Rotate canvas: Quick press/release of the shortcut now align camera with Global-Z. It was only possible in free navigation before.
Timeline scrub: Now respect "limit to frame range" option if activated
Pref register: Code cleanup