This moves the UserAccounts panel to a page in the System panel.
This simplifies a lot of the existing code in the UserAccounts panel.
I did minimal changes to the sub dialogs so that those can be touched
in following changes, making it easier to review this one alone.
The main panel widget is now CcUsersPage, and is an AdwNavigationView
widget that has a default "current_user_page" page. Each page is a
CcUserPage (careful with the one-character difference between these
two classes).
Each CcUserPage has an associated ActUser object.
Commit ffe5aac8 introduced new set of face images and removed the old
ones. Consequently, generic avatar is shown for people after update.
Add back legacy images, so people won't lose their current images on
update. Add them into the subfolder and create symlinks for them,
so it can be simply filtered out from the chooser widget, because just
the new images should be shown.
https://gitlab.gnome.org/GNOME/gnome-control-center/issues/5
