Feature: Add airplane preset and airport specific sector

[SondreBakken]

Atm there is no airplane preset, only helicopters and gunships.

Although you can place the helicopter spawn at the end of a airstrip and add planes into the helicopter preset this is not ideal. Often the airports are not ideal starting positions and there is not enough airstrips for all sides.

WW1 and WW2 scenarios need a more specific airplane / airport feature.

Suggestion:

Add airplane presets.
Make ai spawn airplanes the same way they do with helicopters. (at the edge of the map)

Add sectors at airstrips with a spawn point for airplanes and add "Get airplane" action to the ammobox.