wall half closure control + layers

- add onewaywall option to create a wall if there is not step back
- add layers of maze
- load minetest scheme .we with onewall option

java/org/artisanlogiciel/games/maze/persist/MazePersistWorldEdit.java

@@ -125,6 +125,7 @@ public class MazePersistWorldEdit {
             if ( ground != null )
             {
                 model = getModelFromSlice(ground);
+                model.setOnewaywall(true);
                 System.out.println(model);
             }
             else