model.flight: add FlightPathChunks table to store detailed/splitted flight paths

Will be used for faster PostGIS queries...
model.flight: populate FlightPathChunks table

We add the _full_ flight path to that table. Each row gets 100 points max.

Still needs some filter for path between takeoff/landing only. 100 pts is
a rough guess (250 pts produced slower queries, but smaller tables).
model.flight.FlightPath: add get_near_flights search method

This selects _all_ flights which where near the current flight, but
still uses a large time window. Needs some real distance checks inside
the loop after the query.
model.flight: filter retrieved near flights from database by distance

Prints the detected flights to the console for now...

This could easily be merged with frontend.views.flight._get_near_flights()
model.flight: add meetings table
model.flight_meetings: return a list of meetings, not the query itself
worker.tasks: add find_meetings worker task
model.flight: aggregate flight meetings

Create a new flight meeting only if both aircraft have been separated
for at least 10 minutes.
model.flight_meetings: only return public flights
model.flight_meetings: return a OrderedDict instead of a list
model.flight: disregard early and late fixes
templates/flights/view: show a table of near flights