Hxt tet mesh
This branch mainly introduce changes to Hxt that were already done in the quadMeshingTools branch. I do not wait for that branch to be merged because it does not seem to be mergeable soon.
The only change to Gmsh outside of Hxt are for changing the std::map<MVertex*, int>
to std::map<MVertex*, uint32_t>
in Gmsh2Hxt and Hxt2Gmsh in Mesh/meshGRegionHxt.cpp
and file that were using these functions.