Alpha shapes

Tracking what needs to be done to merge the alpha shape branch into master:

API:

• generateMesh: rethink interface; rethink triangulate and tetetrahedralize at the same time
• createHxtMesh: it should not take an input file, but probably elements and nodes; or simply the contents an existing model; and we should be able to use the other algorithms as well - rethink triangulate and tetetrahedralize at the same time
• alphaShapes, tetNeighbors, alphaShapesConstrained, constrainedDelaunayRefinement, alphaShape: change name to be consistent with the rest of the API

Other:

• test code in GModelIO_STL.cpp
• revert private to public change in discreteFace
• missing copyright in alphaShapes.{h,cpp}
• debug code in meshGFaceDelaunayInsertion.cpp
• handling dependencies in meshGFaceGeodesic.cpp
• revert change involving Extend2dMeshIn3dVolumes() in meshGRegionHxt.cpp