Merge pull request #400 from firedrakeproject/assign_from_indexed_mfs

* assign_from_indexed_mfs:
  Allow assignment into non-mixed FSes from indexed MFSes
Lint fixes
some missing dependencies
Merge pull request #405 from firedrakeproject/build_docs_dependencies

some missing dependencies
add test for mixed Coefficient Piola transforms
Merge pull request #409 from firedrakeproject/test_piola_mixed_fn

add test for mixed Coefficient Piola transforms
missing quote
Merge pull request #408 from firedrakeproject/doc_typo

missing quote
Next attempt at getting the cell right.
turns out vectors are not scalars
missing subscript
Handle OuterProductElements
now with extra testing goodness