Rename setMainKernel to make clear that it isn't a simple setter

apps/gpu/ActuatorLine/ActuatorLine.cpp

apps/gpu/BoundaryLayer/BoundaryLayer.cpp

apps/gpu/ChannelFlow/ChannelFlow.cpp

apps/gpu/DrivenCavity/DrivenCavity.cpp

apps/gpu/DrivenCavityMultiGPU/DrivenCavityMultiGPU.cpp

apps/gpu/DrivenCavityUniform/DrivenCavity.cpp

apps/gpu/MusselOyster/MusselOyster.cpp

apps/gpu/SphereGPU/Sphere.cpp

apps/gpu/SphereRefined/SphereRefined.cpp

apps/gpu/SphereScaling/SphereScaling.cpp

apps/gpu/TGV_3D/TGV_3D.cpp

apps/gpu/TGV_3D_GridRef/TGV_3D_GridRef.cpp

apps/gpu/TGV_3D_MultiGPU/TGV_3D_MultiGPU.cpp

apps/gpu/WTG_RUB/WTG_RUB.cpp

apps/gpu/gridGeneratorTest/gridGenerator.cpp

...lFluidSimulationFactory/VirtualFluidSimulationFactory.cpp

pythonbindings/src/gpu/submodules/parameter.cpp

src/gpu/VirtualFluids_GPU/Parameter/Parameter.cpp

src/gpu/VirtualFluids_GPU/Parameter/Parameter.h

src/gpu/VirtualFluids_GPU/Parameter/ParameterTest.cpp