Blender Git Loki

Sculpt: Pose Squash and Stretch deform mode

This implements squash and stretch as a deform mode for the Pose Brush.
It is similar to scale, but it applies different scale values in different
axis. To achieve this, the pivot local space of the transform needs to
be aligned to the segment when using this deform mode to apply the scale
in the correct direction.

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D7934