Blender Git Loki

Experimental operator to cleanup mask shapekeys

For every shapekey operator check whether mask shape
stays within given tolerance and if so, shapekey is
removing.

TODO:
- Radius and weight are not handled completely crorrect,
need some smarter way to handle them.
- There're huge issues with depsgraph tag update for
mask and acutal mask update -- worked around by manual
call of BKE_mask_evaluate from places where shapekeys
are removing.

Would need to look further into this in trunk.