Improve error messages on client when design docs are not present on couch.
Soledad's CouchDB backend relies on the presence of some design documnts to query/update the user database. The idea is that tapicero will put these documents when it creates the user database right after user registration.
If the design documents are not present on the couch database for some reason, the server will raise a @couchdb.http.ResourceNotFound@ exception and the client will see a 500 error.
We should catch that exception and signal in the client that the problem was missing design documents on the user database on the server.
(from redmine: created on 2014-01-16, closed on 2014-01-20)