Blender Git Loki

Enable (deep) copy of overrides.

This commit enables basic copy of overrides on generic ID level, as well
as from (deep) copy operators for objects and collections.

So e.g. if your linked overridden caracter is in a collection, you can
now (from the outliner) Duplicate that override collection to get a new
overriding copy of the character.

We still need operators (new or modifying existing ones) to handle that
from 3DView e.g.

Note that deep copy code for objects/collections (and incidently
animdata) had to be modified to avoid duplicating/making local IDs that
remain linked ones being used by overrides ones.