This means that the version no longer needs to be passed to every version
manually, and is automatically populated in templates where the parameter is
not explicitly provided.
Whether a user is in transit or not is now determined by an entry in the
in_transit table instead of a dangling checkin.
All completed journeys are stored in the "journeys" table.
This does most of the work needed for automatic checkout. However, note that
the corresponding worker process is not implemented yet.
