Validate OEP ETAs

[erikquinn]

Do some basic math to generate an estimate over the OEP for all aircraft who have filed an oceanic clearance request. Current position, OEP position, calculate distance, then use the groundspeed to get the time.

When combined with #31 to limit to ~45 minutes out, we can reasonably be assured that all aircraft are in level flight, constant speed, aimed roughly right at their entry fix. So they should be quite accurate.

These system-generated estimates can display yellow/red coloring whenever the system estimate and pilot estimate differ significantly, further ensuring the accuracy of the information being used by controllers on nattrak to make decisions on issuing the clearance as requested, or changing altitude, etc. Perhaps a difference of 5 minutes as yellow, 8+ minutes as red.

This mostly serves the purpose of making an obvious indication to the controller that the pilot has submitted an incorrect time, and therefore the time in their request cannot be trusted, and further investigation is needed. Because as it currently stands, a pilot could enter a time that's off by 30 minutes, and unless we eyeball it through vatspy/simaware, there is no way to know that the time was anything but correct.