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/model/HalfSquareRasterModel.java

@@ -1,6 +1,7 @@
 package org.artisanlogiciel.games.maze.model;
 
 import org.artisanlogiciel.games.maze.MovesProvider;
+import org.artisanlogiciel.games.maze.Position;
 import org.artisanlogiciel.games.maze.WallsProvider;
 
 /**
@@ -98,6 +99,12 @@ public class HalfSquareRasterModel
         );
     }
 
+    public short getWalls(Position cell)
+    {
+        return getWalls(cell.getX(), cell.getY());
+    }
+
+
     public short getMoves(int x, int y)
     {
         // moves are where there is no walls ...