2.0: node names are only saved for meshes and materials

I'm not sure if this is intentional or not, but from what I've seen so far, only GLTFMesh and GLTFMaterial call the parent class function `GLTF::Object::writeJSON`, which writes the node name out. I can submit a pull request that fixes this, if it's a bug.

If it is intentional, then perhaps a discussion might be helpful. For me, I expect a format converter to convert my file exactly as possible, and for it to notify me of any changes it had to make, unless I specify otherwise. I've lost multiple days of my time due to various exporters and converts trying to "outsmart" me by "optimizing" my object names, or removing objects it thinks are empty, etc. Luckily at this point I'm prepared for such a thing to happen so I know what to look for, but it's still unexpected behavior in my book.

Start by tracing GLTF::Object::writeJSON and comparing GLTFMesh and GLTFMaterial with the other GLTF object classes that serialize nodes. Verify which object types omit their names, then confirm the completed change preserves node names in the converted glTF output and does not silently remove them.

Written by the indexing model from the issue text.