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.

Have a dedicated visitor for lambda generation from driver

See merge request !170

[bugfix] Correctly iterate over children of MixedElement

See merge request !171

The way we currently iterate over children of mxied elements
was plain wrong for nested mixed elements. The tests that
revealed this will soon follow.

So far, we used a global context to tell the normal visitor,
that it is generating for driver code. This was feasible, as
we only had one differing implementation. With more differences,
it is better style to derive from the visitor and implement
the differences there.

Fix/blockstructured sub element

See merge request !168

Add test cases for hyperbolic problems

Closes #88

See merge request !162

[CI] Raise unit test timeout.

Closes #94

See merge request !167

Merge remote-tracking branch 'origin/fix/raise-default-test-timeout' into feature/hyperbolic-fun-rebased

The previous test timeout of 20s seems to be insufficient sometimes.  Raise it
to 60s.

They are covered in dune-perftool-hyperbolic