Houdini ARAP Deform

This node allows for As-Rigid-As-Possible Deformations using control groups as guides.

It's based on this paper from Olga Sorkine and Marc Alexa:

https://igl.ethz.ch/projects/ARAP/arap_web.pdf

The node setup is based on the original Houdini example file for the linear solver:

https://www.sidefx.com/docs/houdini/examples/nodes/sop/linearsolver/ARAPSurfaceDeformation.html

and has been extended to work with Tetrahedral connectivity.