Add support for vertex normals for meshes, in addition to smoothing groups

I've been doing quite a bit of testing with creating new meshes. I have discovered that although smoothing groups are often very helpful (a useful and very important option), sometimes, even with a well implemented smoothing group generator (from face/vertex normals), incorrect smoothing groups and artifacts are often generated. It would be very useful to be able to explicitly specific face/vertex normals for meshes, in addition to the option of smoothing groups.

Along similar lines, August Lammersdorf of Interactive Mesh notes:
"Even if a 3D file format supports smoothing groups, e.g. 3DS and OBJ (Collada, VRML2, and X3D don't), its use isn't mandatory. Alternatively normals or a crease angle might be delivered. Will JavaFX 3D provide a smoothing group generator utility, as normals are not implemented yet? Otherwise importer/loader have to include such a feature."

(Note that we do have a good smoothing group generator utility for internal testing. However, even with such a smoothing group utility, one does not always get the visual result that one expects, compared to the originally modeled mesh.)