Major Description
Implement support for continuable sessions to keeps state across multiple client/server interactions. Continuable sessions do not require any additional state on the server (i.e. Oak) apart form the apparent repository state.
To continue a session a client would obtain a continuation token from the current session. This token can be used on the next call to Repository.login to obtain a new Session instance that is based on the same repository revision that the session the token was obtained from. Additionally the token could contain information re. authentication so subsequent request can go through a simplified authentication procedure. (asanso's work on OAuth might be of help here.)
Transient changes are not supported in continuable sessions. Obtaining a continuation token from a session with transient changes results in an error.
Continuable sessions are typically short lived (i.e. the time of a single HTTP request). Specifically continuable session do not retain the underlying repository revision from being garbage collected. Clients need to be able to cope with respective exceptions.