Freeze break request: gnome-shell

[Marina Zhurakhinskaya <marinaz redhat com>]

Hi!

I'd like to land the two fixes here:
https://bugzilla.gnome.org/show_bug.cgi?id=659768

The first one ensures that we update the avatar in the chat notification correctly when it changes. The second one ensures that we only remove and re-add the notification icon when it needs to be updated, thereby fixing the new chat notification's behavior of moving down and up when a new message is received. I've tested both changes thoroughly.

Thanks,
Marina