[New Feature]: Support more 'Cesium' data types in 3D

[fcalef]

Checked for duplicates

Yes - I've already checked

Alternatives considered

Yes - and alternatives don't suffice

Related problems

There are lots of new Cesium tile datasets coming out for the Moon and Mars. However, current MMGIS doesn't support rendering either 3D Tilesets as layers OR Cesium .terrain quantized meshes.

Describe the feature request

I want to be able to:
a) load Cesium style .terrain meshes and textures, e.g. from Moon/Mars Trek
b) load Cesium style 3D Tilesets