[Feature Request] Hide gm-style-gtc class when there's only one map type

[leoherzog]

If there's only one map type, we should hide the selector box in the top right next to the compass (gm-style-gtc css class).

With:

Without:

[CounterPillow]

The proper way to do this would be to call setOptions of the overviewer.map options object with essentially the overviewer.mapView.options object but with the mapTypeControl member set to false.

However, Backbone makes the Overviewer JS convoluted enough to make this not a straightforward task.