Rework the whole thing to be API-driven instead of a UI

[evanebb]

This makes it more suitable for what I want to do, and the UI was annoying :)
It's also completely backwards-incompatible and will break existing installations, but I don't care since I am the only one using it as far as I know.

• Removes the UI, adds a REST-ish API in its place.
• Adds support for teams, to allow multiple users to collaborate on repositories under a single namespace.
• Authentication to the API is done through personal access tokens, the same tokens used to obtain a JWT for the registry. The only exception is the endpoint to generate a new token, which can be accessed directly with a username and password (otherwise you'll never be able to access the API).
• Personal access tokens are now hashed using SHA256 with a salt instead of bcrypt. This is because bcrypt is of course slow by design to combat brute-forcing, which isn't ideal since we have to verify the token during every request. Since personal access tokens are generated by the application itself with enough entropy, the security vs speed trade-off is worth it for me :)
• Adds cross-method transaction support to the stores.