There seems to still be some problem.

Note: Not yet working for gmsh files

Not yet implemented:

- Vectorization of quadrature loop
- Anisotropic amount of quadrature points per direction

I also made the order of the terms more consistent and it is now much
easier to compare the skeletons and the boundaries.

Instationary stuff not fixed so far.

There is way more reasons to interpolate a function into the
solution vector and we cover them with one code path:
* Dirichlet boundary conditions (strong ones)
* Initial conditions for instationary expressions
* Initial guesses for Newton solvers

To be honest, I have no idea why this is failing now and not before.
But it makes sense, that the needed divisibility is not present here.

Make anisotropic quadrature order possible for non DG examples.

- Use TensorProductElement in one example.

- We still use the sumfact option to swicth to the sum factorization
  code branch. This way it is still possible to easily swicth between
  sumfact and non sumfact code.

- Only TensorProductElements with the same degree in all directions
  will work. Anisotropie and adaption of quadrature rule will happen
  in the next commits.