To be able to run the admin interface for multiple registries with their own notary sidecars or shared sidecars it should be possible to define a map of registry and related notary server.

e.g.

repos starting with docker.io should use notary.docker.io
repos starting with myregistry.com should use notary.internal.company.com
etc.

This also means more advanced authentication mechanism needs to be put in place #48.