Remove need of passing information about spatial decomposition to contour tree filter

This merge request address issue #713 and removes the need to pass information about the spatial decomposition (block origins, block sizes, block index and blocks per dimension) to the contour tree filter. Block origin information is added to CellSetStructured and the distributed contour tree filter will get this information from CellSetStructured instead of expecting it as parameters to the constructor. Information about blocks per dimension and block indices are computed from the information in CellSetStructure albeit requiring global communication across all ranks. To avoid this communication cost, the caller of the filter can explicitly specify this information via the SetBlockIndices() method.