Need redirect for physdim context after migration from annex to registry

[kirschbombe]

Once the physdim directory is migrated from the annex to the registry, the context url (http://iiif.io/api/annex/services/physdim/1/context.json) will change (http://iiif.io/api/registry/services/physdim/1/context.json). We'll need a redirect so we don't break existing uses of the context.