[editor] glTF import

[kayhhh]

Ability to add glTF models into the world from build mode. Will want drag and drop support eventually but for now just file select a .glb is fine.

How do we send this over the wire? (well, over "The Wired" xD)

Option 1

• typical lattice gltf import -> traverse node and create commands for each item
  • aka split the import into many small atomic events (createNode, editNode, createMesh, etc etc)

Option 2

• a single new "importGltf" event
• how to send gltf model? upload to S3, then send url to it in event?

this also raises the question of storing the model independently on S3, vs merging into the scene like option 1. independent would make more sense if we were using glxf, and in the future maybe we will? It seems to make more sense than a single huge gltf file, but for now we can just merge, seems like the simpler solution