Reformatting for better readability

Remove "pressuresolver." from all classnames to make code more readable.
Improved way of finding BDFM1 dofs on interior facet.

Instead of looking for duplicates in the 18-arity BDFM1 dofmap on each interior facet, use the information in mesh.interior_facets.local_facet_dat to work out the local index of the facet in each of the two adjacent cells.
Simply calculation of map from interior facets to RT1 dofs.

As in the previous commit, use the information in interor_facets.local_facet_dat to identify the local index of an interior facet in the adjacent cells.
Fixed a typo.

Wrong matrix name.
Simply construction from edges to vertices

Use the interior_facets.local_facet_dat map to identify the dof indices of the vertices which lie on each edge.
Simplify lumped mass matrix construction for BDFM1
Fixed typo in comment.

The row vectors store the vectors for an individual SBR field.
Use par_loop for diagonal BDFM1 mass matrix.

When constructing a diagonal BDFM1 mass matrix it is more efficient to use a direct par_loop instead of manipulating numpy arrays.