Merge branch 'walberla2'

.gitmodules

CMakeLists.txt

README.md

cmake/FindwaLBerla.cmake

examples/modular/force_reduction.cpp

examples/modular/force_reduction.py

examples/modular/sd_1.cpp

examples/modular/sd_2.cpp

examples/modular/sd_3_GPU.cu

examples/modular/sd_4.cpp

examples/modular/sphere_box_global.cpp

examples/modular/sphere_box_global.py

examples/modular/spring_dashpot.py

external/walberla

runtime/domain/block_forest.cpp

runtime/domain/block_forest.hpp

runtime/domain/boundary_weights.cpp

runtime/domain/boundary_weights.cu

runtime/domain/boundary_weights.hpp

runtime/pairs.cpp