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/PositionWithDepth.java

@@ -0,0 +1,24 @@
+package org.artisanlogiciel.games.maze;
+
+public class PositionWithDepth
+extends Position
+{
+    private int depth;
+
+    public PositionWithDepth(int x, int y, int depth)
+    {
+        super(x,y);
+        this.depth = depth;
+    }
+
+    public int getDepth()
+    {
+        return depth;
+    }
+
+    public String toString()
+    {
+        return "(" + getX() + "," + getY() + ")" + "/" + depth;
+    }
+
+}