use dbus to register with session manager
remove last use of libegg
remove libegg
panel-shell: convert to a GObject
fix '--replace'

This is broken after switching to dbus for registering with
session manager.

Fix this by setting X-GNOME-AutoRestart to false. In case of crash
GNOME Panel will be autorestarted even with AutoRestart=false.
update all *.ui files