Implement GPS filtering

[wilhelmberg]

continuation from mapbox/mapbox-ar-unity#8

[MiroMuse]

Unity's GPS values (on android) are erratic and use float values from 6 to 4 that cut accuracy (tens of meters), so Willy has been working on a custom android solution (that may be useful for all of our AR SDKs)-- cc @heyadam.

[wilhelmberg]

Android native location plugin PR: #724