[UIFe] New style force-quit window dialog in unity

[Marco Trevisan]

Hi,

Here I am for another UIFe request (sorry, I really don't like
exceptions, but we also need to fix a problematic regression here) for
unity. Basically the "force quit dialog" shown on a frozen window needs
to be moved to Unity, and thus it has been redesigned a little.

See more at:
 - https://bugs.launchpad.net/unity/+bug/1299080

Cheers,
Marco