Fungible token registry

[kantp]

Proposed feature

Establish a registry of deployed fungible token contracts.

Why

The fungible token standard allows Mina users to create their own tokens, and we expect more and more tokens to be deployed. Currrently, there is no easy way to see which tokens exist, and which version of the fungible token standard they are using. That information is required whenever a third party wants to integrate with a fungible token.

It would be useful to have a registry where people can register the token that they deployed. The registry would contain metadata on the token, and where possible verify that the metadata is correct.

Metadata would include the current version of the token contract (i.e., the verification key), the kind of admin contract that is being used (which determines things like the maximal supply, if any, whether the token can be paused, etc.).