Made all traitInfo fields readonly

This came up while working on the new documentation generation and comparing the results to ORAIDE's own code parser.

OpenRA.Mods.Common/Traits/Targetable.cs

@@ -23,7 +23,7 @@ namespace OpenRA.Mods.Common.Traits
 		public readonly BitSet<TargetableType> TargetTypes;
 		public BitSet<TargetableType> GetTargetTypes() { return TargetTypes; }
 
-		public bool RequiresForceFire = false;
+		public readonly bool RequiresForceFire = false;
 
 		public override object Create(ActorInitializer init) { return new Targetable(this); }
 	}