moved device layer to core module
renamed device -> cuda
moved common gpu utility functionality to gpu_private.hpp
removed cu_safe_call.h and cu_safe_call.cpp
fixed build
renamed cuda namespace to cudev
removed static_check.hpp
fixed windows build
fixed source_group
restore cudaSafeCall
fixed compilation warnings
removed blank lines at then end of file
Merge pull request #761 from jet47:gpu-core-refactoring