prepare for hexagon display & other models

- display cell as hexagon is Display.mHexagon if set ( not default )
will need a checkbox to set this
- various new models preparation...

java/org/artisanlogiciel/games/maze/model/HexagonModelProvider.java

@@ -0,0 +1,4 @@
+package org.artisanlogiciel.games.maze.model;
+
+public class HexagonModelProvider {
+}