device orientation controls desktop compatibility

The history behind this is as follows: they have live project that they want to use DeviceOrientationControls with. So I replace:
```javascript
scene.add (mainCamera);
```
with:
```javascript
var mainCameraOrientation = new THREE.Object3D ();
mainCameraOrientation.add (mainCamera);
scene.add (mainCameraOrientation);
...
orientationControls = new THREE.DeviceOrientationControls (mainCameraOrientation);
...
// in the loop
orientationControls.update();
```
This works as expected on iOS v8, *but* on desktop this rotates everything by 90° around X.

So this is what I had to do to make it work in both cases.