add more elements to extruded tests
tidy up feec test, now that enrichment and OPE commute
added new elements to tests
Merge pull request #126 from firedrakeproject/more_extruded_elements

More extruded elements using the FFC 'new_enriched' branch.

Adds extra elements to existing tests, including BDFM, higher order
BDM, and Nedelec elements.