also tabs to spaces

Fix various msvc compiler warnings. With msvc the compiler flags are explicit passed to nvcc with -Xcompiler.

Warning: [-Wbackslash-newline-escape]
https://stackoverflow.com/questions/31673945/clang-backslash-and-newline-separated-by-space-in-single-line-comment

Renmade HOST in GridGenerator to CUDA_HOST because of a name conflict to MPI

Made VF_GPU work with the "new" cmake