Blender Git Loki

Working proof-of-concept of differential override operations.

So, now 'proportional' RNA properties (here, Object's scale) is stored
as 'multiply' override op.

Once again, this is mostly testing for now, there are a lot of potential
issues and traps in current code that'll need more background work to
address later if we keep working in this direction.

Main remaining TODO to complete the proof of concept now is sketching
out a bit of UI/UX control over override!