ui/gtk: Use menu item from stock for full screen

This reduces the required translations and gives a nicer menu
with an icon.

The full screen menu item is no longer a check menu item.
A checked item is not visible in full screen mode,
so it is not needed for this special menu item.

Signed-off-by: Stefan Weil <sw@weilnetz.de>
Message-id: 1361561614-11180-1-git-send-email-sw@weilnetz.de
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
