Closes #13. Boxes are now purrfectly stackable.

cicaprojekt/Wall.java

@@ -30,6 +30,12 @@ public class Wall extends Tile {
         }
     }
 
+    @Override
+    public boolean boxPermission()
+    {
+        return false;
+    }
+
     @Override
     public void onEntry(PlayerBase playerBase) {
         super.onEntry(playerBase);