Move kernel manager into seperate folder

src/gpu/VirtualFluids_GPU/Calculation/UpdateGrid27.cpp

src/gpu/VirtualFluids_GPU/KernelManager/ADKernelManager.cpp

src/gpu/VirtualFluids_GPU/KernelManager/ADKernelManager.h

src/gpu/VirtualFluids_GPU/KernelManager/LBKernelManager.cpp

src/gpu/VirtualFluids_GPU/KernelManager/LBKernelManager.h