Added #if USE_DECLSPEC_PROPERTY condition to control use of
__declspec(property). The -fdeclspec now is not needed to compile using
clang.
Removed use of the IS_INTRESOURCE() macro to the inline method bool
IsIntResource() as the former depends on Windows.h.
The commit only adds the headers and code required by the SpaceMouse
implementation to compile and link. This extract from the 3Dconnexion
SDK is added to the third party directory to allow developers to build without
needing to acquire a cmake enabled version.