CAS-1367: Move spring webflow conversaional state onto the client

Webflow conversations are managed server side in the session. Moving this state to the client with sufficient security would ease the issue with session timeouts and the need for session replication, etc.
Hmmm...probably not so. It would have made sense if we were keeping this new client-side repository as an optional thing, but since it is [and I think it should be] the default it does make sense any more to keep the listener around, right? We no longer deal with sessions anymore.