Merge branch 'clang-tidy' into 'master'

.clang-tidy

.gitlab-ci.yml

...nchmarks/FluidParticleCouplingWithLoadBalancing/Utility.h

apps/benchmarks/GranularGas/check.h

apps/showcases/HeatConduction/ThermalExpansion.h

extern/lodepng/lodepng.cpp

python/lbmpy_walberla/templates/LatticeModel.tmpl.h

python/pystencils_walberla/sweep.py

python/pystencils_walberla/templates/Boundary.tmpl.h

python/pystencils_walberla/templates/CpuPackInfo.tmpl.cpp

python/pystencils_walberla/templates/CpuPackInfo.tmpl.h

python/pystencils_walberla/templates/GpuPackInfo.tmpl.cpp

python/pystencils_walberla/templates/GpuPackInfo.tmpl.h

python/pystencils_walberla/templates/Sweep.tmpl.h

src/blockforest/BlockForest.cpp

src/blockforest/BlockForest.h

src/blockforest/CMakeLists.txt

src/blockforest/GlobalLoadBalancing.h

src/blockforest/Utility.cpp

src/blockforest/Utility.h