SinglyLinkedList: Missing include
DoublyLinkedList: Add Sort()
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. :-)
boot loader: add_safe_mode_settings(): Make parameter const
boot loader: Add safe mode blacklist submenu

It's a browser for the system package content, where entries can be
selected to blacklist them. The selected entries are removed from the
packagefs instance in the boot loader, so that e.g. selected drivers
won't be picked up. The paths are also added to the safe mode driver
settings and will be interpreted when the system packagefs instance is
mounted by the kernel.
Fixed possible bug resulting in not null-terminated string

Signed-off-by: Ingo Weinhold <ingo_weinhold@gmx.de>