Renamed template parameter name.

See merge request walberla/walberla!286

See merge request walberla/walberla!285

The old name (REAL) caused problems when coupling the Trilinos library
since some component has a global define with the same name.

Codegen and cuda

Closes #116

See merge request walberla/walberla!277

use cuda as a first level language in CMake with `enable_language(CUDA)`
enable tests where cuda and codegen are both activated
various minor fixes

Please use mocks for these kind of tests.
a) deterministic
b) faster

get clangtidy10 ready

See merge request walberla/walberla!283

If you are familiar with the coupling feel free to remove the NOLINTs!

I am unsure about const correctness in the python coupling.
If you are familiar with the coupling feel free to remove the NOLINTs!

script to visualize walberla module dependencies

See merge request walberla/walberla!274

[BUGFIX] Jacobi codegen test case

See merge request walberla/walberla!278

drop support for images based on ubuntu 16.04

See merge request walberla/walberla!279

Some fixes in the MSHS benchmark case for parallel execution

See merge request walberla/walberla!280

Refactored the PDF reconstructor test to avoid duplication, extended it by periodicity test

See merge request walberla/walberla!281

accomodate naming in publications

See merge request walberla/walberla!276

Fluctuating MRT: introduce separate relaxation rates

See merge request walberla/walberla!275