Remove further compiler warnings and enables ci job which builds VirtualFluids with warning as errors.

Update to development of using public libraries.

Make the cmake project more flexible while removing the CMAKE_SOURCE_DIR usage.

Remove unused stuff and the global include from VirtualFluidsDefinition.h. Adds missing export includes.

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