Airstrike improvements

This adjusts the way in which flares, cameras, and beacons work:

* Flares spawn when the attack is ordered, and removed 1 second (configurable) after the attack completes.
* Cameras spawn when the attack begins, and removed 1 second (configurable) after it completes.
* Beacons spawn when the attack is ordered, and removed when the attack begins.

It also fixes bombs being rendered through the fog, and fixes flares and cameras being treated as aircraft.