3 different transfer types for Octree to vtkUnstructuredGrid
 1. hanging nodes
 2. conformal grid with pyramids and tets
 3. polyhedral cells (a bit like hanging nodes)
3 different transfer types for Octree to vtkUnstructuredGrid
 1. hanging nodes
 2. conforming grid with pyramids and tets
 3. polyhedral cells (a bit like hanging nodes)
adapted to polyhedral cells
vtkUnstructuredGrid::Reset() has to be called if the mesh is resized
or re-allocated. This is done automatically inside allocateGrid
the octree is now transferred as grid with polydral cells