Blender Git Loki

Py Mathutils: add `invert_safe()` and `inverted_safe()` to `Matrix`.

Those two mimic our BLI invert_m4_m4_safe - they add a small offset to diagonal values,
in case org matrix is degenerated, and if still non-invertible, return identity matrix.

Org patch by me, final enhanced version by ideasman42, many thanks!