0.3 - For VSG 1.0.0

Base OpenXR integration and capability against VSG 1.0.0

Only version 1.0.0 of VSG has been tested - I expect any other versions to cause bugs in vsgvr
(Due to current approach and code duplication in OpenXRViewer.cpp. Watch this space..)

Should also now build as part of vsgFramework / other projects
CMake project is a work in progress - Doesn't have install targets and such yet