Disable shutdown and restart in indicator-session

Disable the "shutdown" and "restart" menu items in indicator-
session, because doing that while you're logged in inside the
chroot wedges your session.  (Unity dies, as does everything except
your gnome-terminal, and your session is stuck in "Ending" state)

Also, let lightdm invoke "reboot" via sudo without a passwd

Add dconf keys and locks to disable the user-background for
the unity-greeter (aka the lock screen), force the background
to MIT, and set a custom "logo" in the bottom right