Implement Project North Star

[BastiaanOlij]

Bit hard to do at the moment without a device, but need to start looking into supporting project north star now that LeapC 4.0.0 is released (already moving to using this).

In order to support this I need to extract the code that handles the message loop and share a single instance of that between instances of objects in our module. See how we do this in OpenHMD for instance.
We can close our message loop once all instances using it have disappeared.

Our GDSensor object can remain our controller for our sensor, but we can now add an ARVR interface that also uses our leap motion driver to obtain head tracking data.

This also means enhancing our GDSensor object to detect whether we're using our in build head tracking and make our positioning a bit more stable.