[!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

python/dune/codegen/__init__.py

@@ -10,3 +10,6 @@ import dune.codegen.loopy.symbolic  # noqa
 import dune.codegen.pdelab  # noqa
 import dune.codegen.sumfact  # noqa
 import dune.codegen.blockstructured  # noqa
+
+# Trigger imports that register finite elements in UFL
+import dune.codegen.ufl.finiteelement  # noqa

python/dune/codegen/ufl/finiteelement.py

+""" Registering finite elements that we have, but FEniCS does not """
+
+from ufl import register_element, L2
+
+
+register_element("Discontinuous Gauss-Lobatto-Legendre",
+                 "DGLL",
+                 0,
+                 L2,
+                 "identity",
+                 (0, None),
+                 ('interval',),
+                 )
+
+
+register_element("Monomials",
+                 "Monom",
+                 0,
+                 L2,
+                 "identity",
+                 (0, None),
+                 ('interval',),
+                 )
+
+
+register_element("L2-Orthonormal Polynomials",
+                 "OPB",
+                 0,
+                 L2,
+                 "identity",
+                 (0, None),
+                 ('interval',),
+                 )
+
+
+register_element("Rannacher-Turek",
+                 "RaTu",
+                 0,
+                 L2,
+                 "identity",
+                 (1, 1),
+                 ('quadrilateral', 'hexahedron'),
+                 )