Add initial implementation for protobuf binary encoding

[weimingzha0]

No description provided.

[weimingzha0]

This is my first PR and my first JS code, so before I implement the full functionality, it's better to make sure it is on the right track. :)

[weimingzha0]

Hi @lutzroeder will this PR be merged?

[lutzroeder]

Ideally there should be a feature using the code for review, to avoid merging code that later isn't tested or used. Model editing is a tricky one, supporting it for one format will likely set expectations that you are working to support and maintain it for many other formats.

[weimingzha0]

yes, I agree that it might set some expectations to support model editing.
To lower the expectation, we can start from low-level libs like pb encoding or other encoding.
When low-level libs are ready for writing, we can further design how to enable the editing via web UI.