[Feature][2.0] Added menu options to allow for ground starts for flights

[phntmknight321]

This is specific to the 2.0 UI. I noticed that at the mission start, and as flights spawned in, they were all air starts, including my player flight (though, I suspect this was user error).

As such, I would like to request the ability to have a menu option to allow for all AI and player flights to be generated from the ground, cold start. For AI units, it would be especially neat if you could see them spawned on the ground, but with a delayed start scripted so that they will sit cold and dark until their designated time sets off the trigger for them to start up and take off to perform their tasking.

Pros:
-Deeper immersion: as you get started up to take off there may be AI flights scheduled to take off with you
-Opens up new strategies and mission types; it could be beneficial to have a mission for airfield strike where you can have the opportunity to destroy the runway, or parked aircraft, to allow for other missions to take place with less of an air threat, or to prevent enemy strike/cas flights from attacking your assets

Cons:
-Potential performance impacts as various flights all come online at different points in the mission
-Scripting difficulty; it isn't TOO hard to get the triggers in place for a delayed start, but magnify that and there could be odd behaviors that crop up
-Balance issues: By having your aircraft, and enemy aircraft all spawned on the ground, it creates edge cases where flights don't have the opportunity to achieve their missions. This is a minor concern, since for immersion sake the benefit outweighs the con here. If your friendly spawned CAP flight gets destroyed before they start up, too bad (in my opinion).