Sessions: Store in the database

Make a simple session-store that saves
the Express / Connect sessions in CouchDB.

As is, this will leave a bunch of dead
sessions in the database, but it's a
starting point.
Fix: Client: Sign out if not on the signin page

If our session is not active, and we're not
on the signin page, sign out and go there.
Sessions: Delete the expired

Perform regular maintenance on our sessions
database, by deleting expired sessions once
every day and then compacting the database.