feat(*): Scalable registry

Allow the deis registry to be scaled across multiple cluster nodes. For now one registry will receive a master lock and only this registry is used by other deis components. All other registries are fast failover slaves in case the node hosting the master registry fails.

This improves app reboot times on node failures.
> Let's stick to one and let the user decide if they want fail-over. :)

:+1: SGTM. As long as we support multiple registries, I think letting the user scale up on their own is preferred.