Types for objects with material properties

[rdeits]

I got partway through writing a .dae file decoder for a robotics project when I started wondering what type to use to store the result. The problem is that we currently assume (in MeshIO and in this package) that the mesh you get from a file is basically always exactly one HomogenousMesh. But what about meshes with textures or material properties? We don't really have a type that encompasses those.

In MeshCat, I have the notion of an Object, which contains a Material and a Geometry, where that geometry could be a HomogenousMesh. Would something like that be useful in GeometryTypes? Or should the mesh type be expanded to allow things like textures or material properties?