Find replacement for TetGen

[allywarner]

Replacement for background lattice tetrahedralization to avoid license conflict.

[jessdtate]

We noticed in our meeting on aug 5, 2021 that tetgen is not built with cleaver and is not called as a library. Ross mentioned that it was for the background mesher, but it appears that cleaver has a simple mesher implemented for the background meshes:
https://github.com/SCIInstitute/Cleaver2/blob/master/src/lib/cleaver/OctreeMesher.cpp
https://github.com/SCIInstitute/Cleaver2/blob/master/src/lib/cleaver/CleaverMesher.cpp
https://github.com/SCIInstitute/Cleaver2/blob/master/src/lib/cleaver/CleaverMesherImpl.h

Furthermore, this seems to be the same in Cleaver 1. We need to follow up with Ross to clarify.