Fix CI python tests with dune 2.9

See merge request !3403

[ci] temporary fix for conflicts with opm cmake setup

See merge request !3415

Fix/istl solvers can communicate

Closes #1229

See merge request !3413

Feature/seq stokes solver

See merge request !3404

Two minor fixes

See merge request !3407

Newer compilers don't include cstdint implicit, we have to
do it explicit.

Feature/helmholtz operator

See merge request !3401

[preconditioners] Add three preconditioners

See merge request !3397

* Thread-parallel Jacobi smoother/preconditioner
* Thread-parallel SOR/SSOR with coloring
* They can be selected via the factory
* They can be used with AMG as smoother (but not unfortunately not via the factory yet)
The reason being that Dune currently hard-coded the selection of available smoothers.
We would have to write our own AMGCreator to include them. Probably better to find an
upstream solution.

Cleanup/partitioningyaspgrid

Closes #1224

See merge request !3394

[ci] Update the ci to use dune 2.9

Closes #1226

See merge request !3399