Fix VRPlugin build with VRPN
When VRPN is enabled and if VRPN has been built in static mode (which is the default), the plugin must be linked with vrpn library but also with VRPN thirdparty library called "quat".
Important notes:
- PV superbuild builds VRPN in dynamic mode and thus this change is not necessary as vrpn lib depends on quat lib.
- current VRPN implementations does not correctly build in dynamic mode with MSVC.
Backport: release