Merge branch 'lbmpy_codegen' into 'master'

apps/tutorials/codegen/02_LBMLatticeModelGeneration.cpp

apps/tutorials/codegen/02_LBMLatticeModelGeneration.dox

apps/tutorials/codegen/02_LBMLatticeModelGeneration.prm

apps/tutorials/codegen/02_LBMLatticeModelGeneration.py

apps/tutorials/codegen/03_AdvancedLBMCodegen.cpp

apps/tutorials/codegen/03_AdvancedLBMCodegen.dox

apps/tutorials/codegen/03_AdvancedLBMCodegen.prm

apps/tutorials/codegen/03_AdvancedLBMCodegen.py

apps/tutorials/codegen/CMakeLists.txt

doc/Mainpage.dox

python/pystencils_walberla/codegen.py