Expose targetline colors to yaml.

All targetlines can now be set to a custom color in yaml or set to be invisible.
All automated behaviours including scripted activities now have no visible target lines.

OpenRA.Mods.Common/Activities/HarvestResource.cs

@@ -109,7 +109,7 @@ namespace OpenRA.Mods.Common.Activities
 
 		public override IEnumerable<TargetLineNode> TargetLineNodes(Actor self)
 		{
-			yield return new TargetLineNode(Target.FromCell(self.World, targetCell), Color.Crimson);
+			yield return new TargetLineNode(Target.FromCell(self.World, targetCell), harvInfo.HarvestLineColor);
 		}
 	}
 }