Feature/#295 remove controller meshes from viewer
This should work in theory, but is not tested on an HMD, yet.
There is now an OpenVRControllerSystem
which makes sure that for each active controller, there is always a corresponding entity (with mesh etc.) in the scene. The OpenVRControllerBehavior
makes sure that it is always a child of the corresponding runtime entity (so it is moved by tracking).
@jwendt @mbellgardt @ademiralp