Reset the VRDisplay between videos

[brandonocasey]

We should reset the VRDisplay position on loadeddata for source changes between 3D videos. This can currently be done for the webvr-polyfill mouse and keyboard controls by using:

window.navigator.getVRDisplays().then((displays) => {
  var display = displays[0];

  display.theta_ = 0;
  display.phi_ = 0;
});

The problem is that there is no standard way to reset the display. So mobile cardboard and touch controls, or native oculus controls won't have the same interface. Maybe destroying it an creating it again somehow would work? This will have to be done with #5