Remove passing the warheads from DamageWarhead to AttackInfo.

Added a Damage class to pass damage value and damage(types) instead.
This removes a great amount of overhead and longterm opens possibilities to have damagetypes without warheads.

OpenRA.Mods.Common/Traits/Multipliers/DamageMultiplier.cs

@@ -26,6 +26,6 @@ namespace OpenRA.Mods.Common.Traits
 		public DamageMultiplier(DamageMultiplierInfo info, string actorType)
 			: base(info, "DamageMultiplier", actorType) { }
 
-		public int GetDamageModifier(Actor attacker, IWarhead warhead) { return GetModifier(); }
+		public int GetDamageModifier(Actor attacker, Damage damage) { return GetModifier(); }
 	}
 }