clean up of communication hiding

CMakeLists.txt

src/GksGpu/BoundaryConditions/AdiabaticWall.cu

src/GksGpu/BoundaryConditions/Periodic.cu

src/GksGpu/Communication/Communicator.cpp

src/GksGpu/Communication/Communicator.cu

src/GksGpu/Communication/Communicator.h

src/GksGpu/CudaUtility/CudaUtility.cpp

src/GksGpu/CudaUtility/CudaUtility.h

src/GksGpu/DataBase/DataBaseAllocatorGPU.cpp

src/GksGpu/TimeStepping/NestedTimeStep.cpp

targets/apps/GKS/MultiGPU/MultiGPU.cpp

targets/apps/GKS/MultiGPU_2D/MultiGPU_2D.cpp