Added cuda and mpi library (Closes #20)

To further improve reusability and to decouple VF domain logic from cuda and mpi, this MR add two new libraries to VF.

cuda Extracted some general cuda functionality from VirtualFluidsGPU and GridGenerator. This includes CudaTimer, CudaGrid and DeviceInfo. Refactored DeviceInfo: potential errors while accessing the device datas are propagated.

mpi Here i just extracted the Communicator classes from VirtualFluidsCPU, as they were very generic without any logic to VirtualFluids domain logic. VirtualFluidsGPU still has its own Communicator, as this Communicator depends on a GPU layout. But there is also some redundant code, which could be removed in the future. Besides some refactorings in the communicators to make them thread safe.