HexReferenceSpace seems to Work: other test passed -- ReferenceSpace and PermutationTree: need to compress tag if they do not form a continous sequence -- HexNodeBasis: reworking with new framework -- PermutationTree: start serialization

git-svn-id: https://geuz.org/svn/gmsh/trunk@16579 59c8cabf-10d6-4a28-b43f-3936b85956c4