Idea: Add ability to load an MRE scene from json-formatted scene description file

[eanders-ms]

Companion piece: Develop a Unity exporter to export a scene to json.

• Give user choice to export objects to glTF or leave them as asset bundles.

Update: this is just loading a gltf.

[stevenvergenz]

Or better still, initialize an app from an A-Frame document ;)

[stevenvergenz]

First attempt: https://github.com/AltspaceVR/aframe-as-mre