Computes tensor index from single index.

This should probably be part of the loopy Mapper but I'm not sure if I could add it there.

This should probably be part of the loopy Mapper but I'm not sure if
I could add it there.

Moves application of transformation from micro to reference element from visitor to PDELab interface

Removes micro_to_macro_index from accum_insn and introduces a class BlockstructuredAccumulationSpace to specialize AccumulationSpace for blockstructured FEM

Unrolling the dimension loops broke the diagonal_jacobian
transformation since it was looking for index_sums over certain
expressions.