Post-hoc UI freeze break request

[Giovanni Campagna <scampa giovanni gmail com>]

I'm sorry I pushed the commit before asking first, I totally forgot of
the freeze. I'm ok with reverting if the freeze break is not accorded.
What I'm asking the permission to implement the designs in
https://bugzilla.gnome.org/show_bug.cgi?id=682540, which is listed as
priority 0 in https://live.gnome.org/ScreenLock/BoF.
It consists of merging the volume, network and battery indicator in
the lock screen in one menu.

While we're there, the following bugs are open for the screen lock
feature, and affect UI:
- https://bugzilla.gnome.org/show_bug.cgi?id=682542 (makes the a11y
menu reappear in the unlock dialog)
- https://bugzilla.gnome.org/show_bug.cgi?id=682546 (shows the user
name on the left with a padlock)
- https://bugzilla.gnome.org/show_bug.cgi?id=682544 (replaces auth
failed notifications with orange messages)
- https://bugzilla.gnome.org/show_bug.cgi?id=682285 (replaces the drag
handle with three animating arrows)
They all have patches, so I hope they'll be finished before 3.6. I'll
send separate requests for each of them in due time however.

Thank you,

Giovanni