Ability to use elements to manipulate nodes in a model element's three.js tree (f.e. a lume-gltf-model's tree)

[trusktr]

Something like the following that will find a Three.js node with the name some-node and apply a custom material to it, in this case a phong material with color skyblue, so that we don't have to write custom Three.js code outside of the HTML to customize a model's materials:

<lume-model-modifier name="some-node" has="phong-material" color="skyblue">
  <lume-gltf-model src="foo.gltf"></lume-gltf-model>
</lume-model-modifier>