Remote session support needs to be able to start systemd units
and also manage gnome-remote-desktop.
This commit adds a polkit policy to accomodate both subactions
with one overarching action that only needs to be unlocked one time.
- 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
