Blender Git Loki

Dynamic Override: Share a tiny bit more code betzeen dynamic and static overrides.

Renamed dynamic's override_mode to 'operation' (same as with static) and
made it use same enum values.

Note that ultimately/ideally both would only use one data structure,
this should be manageable and will simplify RNA apply code (which is to
be shared by both), but that kind of cleanup/refactor we can do once we
have a working system, just before merging into blender2.8.