Support undo of delete

[Erick Pérez Castellanos <erick red gmail com>]

Finished the support for undo operation in Gnome-contacts, the patch is
upload in the [bug
657975](https://bugzilla.gnome.org/show_bug.cgi?id=657975)

The patch include adding a Gtk.Overlay right below Gtk.Window of
Contacts, and the Grid inside it. Set the color of the Gtk.overlay
background to transparent, and course will work with newer gtk+ versions
from git.

Here there's some thing missing design tough, like what to do when two
notifications are shown at the same time, how to stack it ?, or should
be shown one after the other ?.
Anyway, the use of this kind of notification need design if it gonna
spread through the application.
For now, that's not handled at all, so please don't delete contact too
fast, cause you're gonna miss the notification.