Move walberla app generation files to own repo

src/pystencils_autodiff/CMakeLists.tmpl.txt

...encils_autodiff/framework_integration/texture_astnodes.py

src/pystencils_autodiff/graph_datahandling.py

src/pystencils_autodiff/simulation.py

src/pystencils_autodiff/walberla.py

src/pystencils_autodiff/walberla_main.tmpl.cpp

src/pystencils_autodiff/walberla_user_defintions.tmpl.hpp

tests/test_walberla.py