refactoring, deploy Position and XYGridIterator

- try to use more Position instead of (x,y)
  - create PositionWithDpeth for its specific usage in path finding
- create a XYGridITerator that walk cells from grid X then Y.

java/org/artisanlogiciel/games/maze/gui/Display.java

@@ -66,6 +66,11 @@ implements StatusListener
         maze.resetCellRenderer(hexagon, frameSize);
     }
 
+    public void setBackground(boolean background) {
+        addStatus(background ? "view background" : "hide background");
+        maze.setViewBackground(background);
+    }
+
     private class MazeFrame extends JFrame
     {
         MazeFrame(LabyModel model, WidthHeightProvider frame, MazeParams params) {