Add ICAO to for all queries

[E3V3A]

We want to be able to also use the ICAO codes for searching flights and airports, because many smaller airports do not have a IATA code as they don't serve the general public airliners or doesn't have internet connection to their flight data.

• https://upload.wikimedia.org/wikipedia/commons/a/ab/ICAO_FirstLetter.svg

The first letter are according to this map:

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We can either download the entire ICAO database or check if there is a f24 query for this.

• https://github.com/jpatokal/openflights/blob/master/data/airports.dat

There airports with no IATA, has the \N in the field for IATA, and sorted on ICAO.

There are 4701 airports without an IATA code!