schemas: Add 'avatar-directories' setting
gnome-control-center and gnome-initial-setup uses the default faces dir for user avatar defined by $datadir/pixmaps/faces/ that's were the gnome-control-center install the faces images.
This new setting will allow to change the default faces in both projects only changing this setting without the need to patch gnome-control-center.
Edited by Georges Basile Stavracas Neto