Add menu plumbing for the new map editor.

OpenRA.Game/Game.cs

@@ -375,6 +375,11 @@ namespace OpenRA
 				ModData.LoadScreen.StartGame(args);
 		}
 
+		public static void LoadEditor(string mapUid)
+		{
+			StartGame(mapUid, WorldType.Editor);
+		}
+
 		public static void LoadShellMap()
 		{
 			var shellmap = ChooseShellmap();

OpenRA.Game/World.cs

@@ -22,7 +22,7 @@ using OpenRA.Traits;
 
 namespace OpenRA
 {
-	public enum WorldType { Regular, Shellmap }
+	public enum WorldType { Regular, Shellmap, Editor }
 
 	public class World
 	{