Add delay and full duration support to beacons

Previously, support power beacons were hardcoded to unlimited duration and
then cleaned up directly by the support power. This is problematic if we
want the beacon to remove itself after a certain delay, though.

OpenRA.Mods.Common/Traits/SupportPowers/AirstrikePower.cs

@@ -176,7 +176,7 @@ namespace OpenRA.Mods.Common.Traits
 						Info.ArrowSequence,
 						Info.CircleSequence,
 						Info.ClockSequence,
-							() => 1 - ((distanceTestActor.CenterPosition - target).HorizontalLength - info.BeaconDistanceOffset.Length) * 1f / distance);
+						() => 1 - ((distanceTestActor.CenterPosition - target).HorizontalLength - info.BeaconDistanceOffset.Length) * 1f / distance);
 
 					w.Add(beacon);
 				}