Add a location listener

[ljbade]

Currently the app can poll getMyLocation but we should have a location listener.

[tobrun]

I need to this for User tracking sample.

Location is always null in onCreate method.

Location location = mMapView.getMyLocation();
if (location != null) {
    mMapView.setZoomLevel(8);
    mMapView.setCenterCoordinate(new LatLng(location));
}

Required to listen async to location updates.

[ljbade]

@tobrun should be easy to whip up then, move this to 2.1.0?

[ljbade]

@tobrun this will be in my UserLocationView refactor