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.
the go-based registry may not address that issue, but that is a valid point. Let's stick to one and let the user decide if they want fail-over. :)

@carmstrong sounds good to you?