CUDA code refactored to multiple files

CMakeLists.txt

src/FluidSimulation.cpp

src/cuda/include/PCISPH_CUDA_interface.h

src/cuda/include/cuda_device_vars.h

src/cuda/include/float3_helper_math.h

src/cuda/include/init_cuda.h

src/cuda/include/pcisph_kernels.h

src/cuda/include/pcisph_update.h

src/cuda/include/smoothing_kernels.h

src/cuda/include/spatialHash_NBSearch_kernels.h

src/cuda/init_cuda.cu

src/cuda/kernels_cuda.cu

src/cuda/pcisph_kernels.cu

src/cuda/pcisph_update.cu

src/cuda/smoothing_kernels.cu

src/cuda/spatialHash_NBSearch_kernels.cu