Probably the final Fix#97
Unused aircraft (assigned upon takeoff) would get claimed but since it's not possible to delete those flights after aborting, these flights wouldn't get released anymore. This should fix that issue, including a migrator change to correct the number of claimed aircraft per squadron.
Would cause an exception because `PackageWaypoints.create(p, c)` would call `package.departure_closest_to_target()` on its turn which raises a runtime exception if no flights are present. Makes total sense when you think about it...
Fixes#66
Attempts to fix incompatibilities in save files across builds. The idea is to try and handle the incompatibility as graceful as possible, and adding more "incompatibility fixes" in the future.
