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

The indexing information needs to be stored and reset
for visiting of the second branch.

After a lot of experimenting and stuff...

not in CMakeLists.txt