Blender Git Loki

Depsgraph: Re-use evaluated mesh across frames and remove time dependency from all CoW components

This commit is a work forward having less updates during playback, which speeds
things up a lot here. The idea is simple: stop update all copy-on-write
datablocks (which implies full re-evaluation actually) on frame change and
re-use existing evaluated meshes as much as possible.

This brings playback speed to 24 fps on the dino test scene here. Performance
drops down a lot when armature is animated tho, but that's because of need of
tangent space calculation which we can't do much about from just a dependency
graph.

Hopefully this doesn't make copy-on-write too unstable, quick tests here are
surviving fine.