codegen cmake: add to PYTHONPATH instead of overwriting

See merge request walberla/walberla!300

Make codegen cmake integration symlink-compatible

See merge request walberla/walberla!301

[BUGFIX] missing executables

See merge request walberla/walberla!296

Since some benchmarks/tutorials are registered as tests they have to be
built in order to run.

Allowed different field layouts in LBM codegen

Closes #119

See merge request walberla/walberla!294

Added warning if no SIMD instruction could be determined, adapted field layouts in all tests and benchmarks

FFT: show error when using with MPI_COMM_WORLD

See merge request walberla/walberla!293

enable mesa_pd codegen for ci

See merge request walberla/walberla!292

heat conduction and thermal expansion showcase

See merge request walberla/walberla!284

moved coverage image to local registry

See merge request walberla/walberla!291

Moved from heat capacity to specific heat
to take into account individual mass of a particle.

Use serial I/O instead of MPI-IO for certain versions of OpenMPI

See merge request !282

removed mrt3 from each test case

See merge request walberla/walberla!287

optimize build time

See merge request !290

enable clang10

See merge request walberla/walberla!288

Renamed template parameter name.

See merge request walberla/walberla!286

See merge request walberla/walberla!285