GoogleVR SDK Plugin + GoogleVR bridge library

[JeroMiya]

Google has a new GoogleVR SDK, their replacement to the Cardboard SDK that theoretically supports both cardboard devices and Daydream devices. Create a plugin for the GoogleVR SDK (native version of the SDK). This should provide a tracker for /me/head for the head tracking and /me/hands/left and/or /me/hands/right. It should also provide some button interfaces and analog interfaces for their simplified controller API.

As part of this work, there needs to be a bridge library for the GoogleVR SDK. This library would need to allow the user to optionally pass in a GoogleVR context that the OSVR plugin will use, as well as retrieve the current context that is set. This will allow sharing of the context between the client application and OSVR, such that the user can still use the GoogleVR audio SDK (beyond the scope of OSVR) or the GoogleVR compositor (no pass-through compositor support yet in RenderManager), as needed.