- refresh the symbolic icons to sync some style changes and update the source sheet
- rename assets for the privacy subpanel's symbolic icons
- delete deprecated/unused symbolic icons
- add new icon for system panel
- add new icon for remote desktop so it isn't using displays icons
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.
