Fixes 1521 - Add conspicuity and listening codes

[ThomasSaunders]

Fixes #1521

Summary of changes

Adds listening and more conspicuity squawks for code callsign conversion.

[Liaely]

Can you change 0043-0045 from generic 'UKP' as with the other ones?

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Also, I'm not too sure on the labelling for NATO Air Policing (Air Defence Priority) flights, open to hearing opinions on that front.

[ThomasSaunders]

The AIP doesn't have specific callsigns unfortunately for UKP.

Put NATO on there as they're used for QRA stuff, a prompt to the ATCO that they're a higher priority flight. Happy to remove though.

[ThomasSaunders]

Thinking more about it, would the generic UKP (and maybe HLE?) be better as a label than C/S? I went with C/S to reflect what I know to be reality but might be an occasion where deviating may be a better course of action?

[Liaely]

I think if someone is using a special squawk code for a specific air ambulance, etc, as specified in the AIP, then it's worth it to keep it with the callsign.
As for the specific police ones, I see that point, so probably better to keep it as generic UKP instead of UKP251/252/37.

WRT ADP flights, on VATSIM, no flight can declare itself to have priority, but that doesn't stop the use of callsigns/squawks appropriate to the 'mission' that may be being flown. I have some thoughts in regard to that, but moreso I don't think that 'NATO' would be the best label for them, as that implies generic NATO stuff, whereas something else may be better matched to the squawk.

[ThomasSaunders]

All makes sense, I'll leave UKP as it is for now then.

For NATO, perhaps AIRPOL or similar (Air Police) is better? I believe this is the primary use for the squawks.