3.6 Feature: User panel improvements

[Matthias Clasen <matthias clasen gmail com>]

This feature was originally targeted for 3.4, but didn't make it.
Initially, it was only about making the user panel aware of Kerberos
identities, and handling ticket expiration. It has grown in scope, as
we are now also aiming for nicely integrated AD/LDAP enrollment. Thus,
the title is a bit of a misnomer now.

This mainly affects the user panel in the control center (where we
want to show suitable things when we find ourselves in a centrally
managed system), gnome-settings-daemon (which will grow a plugin to
ask for passwords if a ticket expires and can't be automatically
renewed) as well as gdm and the proposed initial-setup tool.

You can read more details here:
https://live.gnome.org/ThreePointFive/Features/UserPanel

Ray Strode and Stef Walter are working on this.