[!322] Register PDELab finite elements into UFL

Merge branch 'feature/fenicsesque-finite-elements' into 'master'

ref:extensions/dune-codegen TODOs:

-   [x] Register all finite elements from PDELab into UFL
-   [ ] Adapt driver generation so that they are actually used
-   [ ] Adapt examples to be more precise about the basis they are using

See merge request [extensions/dune-codegen!322]

  [extensions/dune-codegen!322]: gitlab.dune-project.org/extensions/dune-codegen/merge_requests/322