Re-implement streaming support

[Moguri]

With glTF 2.0, we've lost streaming support. It looks like glTF 1.0 also no longer works for streaming due to the new reference system (e.g., we cannot update an object without updating the mesh too). This issue is to track discussion on a more formal streaming API for blendergltf. We'll need to figure out:

• blendergltf API for streaming data (e.g., how to handle partial updates)
• glTF 2.0 extension to facilitate streaming (BLENDER_streaming)?
  • glTF 1.0 used string keys to identify objects, which made it possible to still find an object to update if the client tracked keys. Now they are indexes in glTF 2.0, so we need a new identifier to use.
• Do we implement the extension to work with both glTF 1.0 and 2.0?
• What kind of utilities (if any) do we want to bake into blendergltf to help facilitate streaming? Currently all logic for streaming is in BRTE. Does it make sense to move anything from BRTE to blendergltf? I think likely not, but it is worth exploring.

[Moguri]

The BRTE project is now defunct, and BlenderPanda (the only known user of BRTE) no longer streams partial updates. I am closing this issue since I am the one that opened it, and I no longer need it. If anyone else is interested in this feature, we can re-open this issue.