Improve naming of API endpoints

[wslyvh]

The current naming of the API endpoints seem confusing and don't really follow best practices.
Good API designs can improve the developer experience, making integrations more recognizable, faster and easier.

Since the development of the API still seems in early stages, it might be better to reconsider now before having to deal with backwards compatibility.

From what I understand the main resource here is registry which contains communities (or 'scores')
I'd suggest to use consistent naming. Scores and communities are somewhat confusing at the moment.

For the API, I'd propose the following..

Not sure if this is something that's supposed to be public, but I'd add
GET /registry - for an overview of all the registered communities.

Rename
GET /registry/signing-message -> GET /registry/nonce
POST /registry/submit-passport -> POST /registry/score/{community_id}

These remain the same
GET /registry/score/{community_id}
GET /registry/score/{community_id}/{address}