Update database so that route data is stored against individual flights, not as reference data.

[tomcarman]

Issue

• Currently route data is stored in a route_data table, which is refreshed periodically from the routing API, at a maximum interval of 60min per callsign.
• This data is then joined (via callsign as a key) with data in the aircraft_data table to generate route statistics. (Note: It is also used in the AboveTimeline component to display route data for aircraft in close proximity - this will need some minor modifications as part of this update)
• This approach is flawed, as callsigns are not consistently bound to the same route; their associated route may change over time - hence the current periodic refreshes from the routing API.
• This means that currently, when route statistics are generated, and rows in aircraft_data are joined with route_data, the "most recent known route" for that callsign is attributed to the flight - but at the time of the flight that callsign could have had a different route associated.

Fix

• Expand the aircraft_data table to store the route information inline against the flight.
• Continue to maintain the route_data table, but treat it as a "cache" of recently seen routes (to avoiding always calling the routing API).
• Update the existing implementation to store route data into the new columns in aircraft_data.
• Decrease the frequency which callsigns are re-fetched from the routing API from 60min to 120min to reduce load.
• Create a migration script for existing users, so that route data is copied for existing flights, from the route_data table to the newly added columns in the aircraft_data table. This accepts that historic flights will just receive the most recent route assigned to that callsign - if this was different at the time the flight was originally captured, that is now lost data, as it is in the existing implementation.