Create a new AppSkeleton as base class of RiftSkeleton and move in all the VR-independent state.
Moved constructor initialization of scenes into base class.
Move FlyingMouse destruction to base class.
Move _DrawScenes function into base class.
Init id matrix uniforms using glm::mat4.
Move some GL initialization functionality to base class.
Move variable decl near first use.
Add a getRTSize function to tease apart the render viewport from the OVR SDK.
Use the new accessor function to set viewport in display_raw.