Support 'inaccuracy' on effect warhead

Purely cosmetic, allows to 'fake' slight inaccuracy without
affecting game balance on weapons like light machine guns.

OpenRA.Mods.Common/Warheads/CreateEffectWarhead.cs

@@ -46,6 +46,9 @@ namespace OpenRA.Mods.Common.Warheads
 		[Desc("Whether to consider actors in determining whether the explosion should happen. If false, only terrain will be considered.")]
 		public readonly bool ImpactActors = true;
 
+		[Desc("The maximum inaccuracy of the effect spawn position relative to actual impact position.")]
+		public readonly WDist Inaccuracy = WDist.Zero;
+
 		static readonly BitSet<TargetableType> TargetTypeAir = new BitSet<TargetableType>("Air");
 
 		/// <summary>Checks if there are any actors at impact position and if the warhead is valid against any of them.</summary>
@@ -109,6 +112,9 @@ namespace OpenRA.Mods.Common.Warheads
 			var explosion = Explosions.RandomOrDefault(world.LocalRandom);
 			if (Image != null && explosion != null)
 			{
+				if (Inaccuracy.Length > 0)
+					pos += WVec.FromPDF(world.SharedRandom, 2) * Inaccuracy.Length / 1024;
+
 				if (ForceDisplayAtGroundLevel)
 				{
 					var dat = world.Map.DistanceAboveTerrain(pos);