Blender Git Loki

Gizmo: use spin widgets by default

- Now the spin tool has a persistent gizmo.
- Uses scene orientation, with additional view orientation.
- Uses the cursor center, ignoring the pivot since the
selection center is rarely useful.
- Disable most of the redo gizmo's for now since they overlap,
only allow adjusting the angle.

Note: mixing new action with adjusting previous is confusing,
we'll want to have design guidelines regarding this.