Near flight

Proof of concept. Mimics the 'MeetingPoint' feature of OLC. Queries are quite fast, but might suffer from uncached tables (and they grow huge very fast now, FlightPath table has 750 MB for 6000 flights on my test system).

Still lacks of some important features, so definitly not ready for production yet.

If someone want's to test it: upgrade database, run "manage.py flights update-flight-paths --force", enjoy.