Composition operations

Created by: pabloriera

This includes composition operations named like this

For dense Array{S,4}

dense_composition_kron

for state first ordering

dense_composition_matmul

for label first ordering

For sparse representation COO(2,2) of COO(2,2)

sparse_composition_kron

for sparse state first ordering

Now I am working on sparse label first ordering, but it implies writing CSC/R matmat mul from scratch.

Caveats:

There is a lot of unbeautiful code, some new types or properties missing to make it more julianesque, let me know the proper way to fix this.