Fix Outflow Boundary

python/lbmpy_walberla/additional_data_handler.py

python/lbmpy_walberla/boundary_collection.py

python/lbmpy_walberla/packing_kernels.py

python/lbmpy_walberla/storage_specification.py

python/lbmpy_walberla/sweep_collection.py

python/lbmpy_walberla/templates/BoundaryCollection.tmpl.h

...lbmpy_walberla/templates/LbmStorageSpecification.tmpl.cpp

...n/lbmpy_walberla/templates/LbmStorageSpecification.tmpl.h

python/lbmpy_walberla/walberla_lbm_package.py

python/pystencils_walberla/additional_data_handler.py

python/pystencils_walberla/boundary.py

python/pystencils_walberla/templates/Boundary.tmpl.h

python/pystencils_walberla/templates/SweepCollection.tmpl.h