Double-click CesiumGeoreference to teleport editor camera to the origin

[nithinp7]

I think it would make a lot of sense for the CesiumGeoreference actor to have some sort of invisible billboard so that it can be double-clicked in the world outliner to teleport the editor camera to the origin (or maybe close enough to be looking at it). There is almost certainly a painless way to do this, but if not we should at least be able to override the focus actor event like Bao did here: #231.

[argallegos]

It would actually also be good to add an editor gizmo to it like other non-rendering actors have:

I think it would be a good UX improvement to help users understand where the world origin 0,0,0 is. It might as a side effect help with teleporting the editor camera.