This new function does the actual generation using pystencils and creates a target library that can be used as a dependency as usual. One should not list the python script itself anymore in add_executable.
Convention: Use the AppName as a prefix for the generated lib!

Example Usage:

waLBerla_generate_target_from_python( NAME AppNameGeneratedLib FILE GenerateKernel.py OUT_FILES Kernel.h Kernel.cpp)

waLBerla_add_executable ( NAME AppNameGeneratedLibTest DEPENDS GeneratedLib)

- proper escaping of braces when passing JSON to python
- pass information if walberla was built with CUDA to pystencils
  to support apps that use GPU optionally

- information from CMake to codegen: double/float, OpenMP, ...

- one python file can now generate multiple source files

- Add generator files to targets to show them in VS solutions
- mark generated files as such in CMake

If you have access to the old closed source waLBerla repository, you may restore the complete history with the following command
git fetch git@i10git.cs.fau.de:software/walberla.git 'refs/replace/*:refs/replace/*'