added support for nuke launch sound to confirm strike

separated into IncomingSound = "nuke approaching/detected"
and changed LaunchSound into "nuke lauched"

also nuke with small L .aud in cnc rules looks like a typo

OpenRA.Mods.RA/SupportPowers/SupportPower.cs

@@ -27,6 +27,7 @@ namespace OpenRA.Mods.RA
 		public readonly string EndChargeSound = null;
 		public readonly string SelectTargetSound = null;
 		public readonly string LaunchSound = null;
+		public readonly string IncomingSound = null;
 
 		public readonly bool DisplayTimer = false;