boot loader: Menu[Item] API improvements

* Make Menu and MenuItem polymorphic.
* MenuItem:
  - Make SetMarked() virtual, so it can be overridden.
  - Add SetSubmenu() and Supermenu().
  - Delete the submenu in the destructor.
* Menu:
  - Add Entered()/Exited() hooks. They frame the time the user navigates
    the menu or any of its submenus. The hooks allow for subclasses
    populating their item list dynamically.
  - Add SortItems().
* Update boot loader menu copyright text to include 2013, now that it is
  over soon. :-)

headers/private/kernel/boot/menu.h

@@ -30,12 +30,12 @@ class MenuItem : public DoublyLinkedListLinkImpl<MenuItem> {
 public:
 								MenuItem(const char* label = NULL,
 									Menu* subMenu = NULL);
-								~MenuItem();
+	virtual						~MenuItem();
 
 			void				SetTarget(menu_item_hook target);
 			menu_item_hook		Target() const { return fTarget; }
 
-			void				SetMarked(bool marked);
+	virtual	void				SetMarked(bool marked);
 			bool				IsMarked() const { return fIsMarked; }
 
 			void				Select(bool selected);
@@ -57,7 +57,11 @@ public:
 			char				Shortcut() const { return fShortcut; }
 
 			const char*			Label() const { return fLabel; }
+
 			Menu*				Submenu() const { return fSubMenu; }
+			void				SetSubmenu(Menu* subMenu);
+
+			Menu*				Supermenu() const { return fMenu; }
 
 private:
 			friend class Menu;
@@ -93,10 +97,13 @@ enum menu_type {
 class Menu {
 public:
 								Menu(menu_type type, const char* title = NULL);
-								~Menu();
+	virtual						~Menu();
 
 			menu_type			Type() const { return fType; }
 
+	virtual	void				Entered();
+	virtual	void				Exited();
+
 			void				Hide() { fIsHidden = true; }
 			void				Show() { fIsHidden = false; }
 			bool				IsHidden() const { return fIsHidden; }
@@ -131,6 +138,9 @@ public:
 			shortcut_hook		FindShortcut(char key) const;
 			MenuItem*			FindItemByShortcut(char key);
 
+			void				SortItems(bool (*less)(const MenuItem*,
+									const MenuItem*));
+
 			void				Run();
 
 private: