support for keeping vox objects as seperate meshes

[tastesliketriangle]

I've been using MagicaVoxel to make tiles for my Gridmaps. when exporting from MagicaVoxel to .OBJ files, all the voxel objects are seperate(i'll usually bundle them into a .GLTF file. but this importer merges the meshes together, which makes it completely useless for making Gridmaps.

[CloneDeath]

Would you want to import each disjoint (not touching) group of voxels as a separate mesh I'd support that PR.

An alternative would be to have each tile be in a different group, and then have the importer have an option "split top level groups into different meshes". I don't know about the details of that... like, how extensions like flip and reference group would work... but either way, if someone comes up with this sort of solution, I'd also support that PR.