This is needed so manipulators can tag themselves for removal
without causing problems from freeing data within a callback.
Also use properties within the dial manipulator and fix an error where
removing a wmManipulatorGroupType didn't remove its keymap.
While this is work-in-progress from custom-manipulators branch
its stable so adding into 2.8 so we don't get too much out of sync.
- ManipulatorGroupType's are moved out of the manipulator-map and are now
global (like operators, panels etc) and added into spaces as needed.
Without this all operators that might ever use a manipulator in the 3D
view would be polling the viewport.
- Add optional get/set callbacks for non-RNA properties
Needed so re-usable manipulators can control values that
don't correspond to a single properly or need conversion.
- Fix divide by zero bug in arrow manipulator (when moving zero pixels).
Sync with custom-manipulators branch
- Use identifiers for properties.
- Property array index access.
- Remove operator from manipulators
(wasn't used and will likely add in a different way).
As with operators, the window-manager has the API for defining,
the editor can implement and register its own manipulators.
This exposes wmManipulator, keeping it opaque isn't
practical if editors and Python are to implement their own.
