Sparsity builder uses custom struct cmap instead of op_map
Added offset to cmaps.
Purge OP2-COMMON dependency
Make plan related cython code into a separate extension
Refactor C/C++ extensions
 - split into 3 extensions (sparsity, plan, computeinds)
 - include sparsity C++ code directly in cython
Refactor, move Plan class from module device to module plan