RideItem separation of concerns

.. instead of making the caller keep rideitem up to date etc
   we are going to move to it looking after itself.

.. the first part of this is to make it responsible for checking
   if it is stale and computing fingerprints etc

.. the next part will be making it responsible for refreshing
   the cached values.

One big thing too:

.. the fingerprint is now based upon the zone config that applies
   for the date of the ride -- not all zone config. So if the config
   changes but not for the date of this ride (e.g. set a new CP starting
   from today) then the old data does not get marked as stale.