Make MP start units facing customizable

There might be modders or mappers who prefer different initial facing settings than the hardcoded ones.

OpenRA.Mods.Common/Traits/World/MPStartUnits.cs

@@ -37,6 +37,12 @@ namespace OpenRA.Mods.Common.Traits
 
 		[Desc("Outer radius for spawning support actors")]
 		public readonly int OuterSupportRadius = 4;
+
+		[Desc("Initial facing of BaseActor. -1 means random.")]
+		public readonly int BaseActorFacing = 128;
+
+		[Desc("Initial facing of SupportActors. -1 means random.")]
+		public readonly int SupportActorsFacing = -1;
 	}
 
 	public class MPStartUnits { }