Change numbering of sub-entities?

[mscroggs]

Currently, sub-entities of the reference cell are numbered following the UFC convention on simplex cells:

When the vertices have been numbered, the remaining mesh entities are numbered within each topological dimension based on a lexicographical ordering of the corresponding ordered tuples of non-incident vertices.

However non-simplex cells instead are ordered by incident vertices. This matches the convention used by DefElement:

This inconsistency is a little confusing. I propose that we update the numbering of sub-entities on simplex cells so that all cells match the DefElement conventions