Fewer auth dialogs for Print Settings

The latest version of system-config-printer adds a new button to the main screen: Unlock. This is a GtkLockButton attached to the “all-edit” polkit permission for cups-pk-helper.

The idea is to make it work a bit more like the Printing screen in the GNOME Settings application. To make any changes you need to click Unlock first, and this fetches all the permissions you need in order to make any changes.

This is a change from the previous way of working. Before this, all user interface elements that made changes were available immediately, and permission was sought for each change required (adding a printer, fetching a list of devices, etc).

Hopefully it will now be a little easier to use, as only one authentication dialog will generally be needed rather than several as before.

Exceptions are:

• the dialog for reading/changing the firewall (when there are no network devices discovered but the user is trying to add a network queue), and
• the dialog for adjusting server settings such as whether job data is preserved to allow for reprinting

These are covered by separate polkit permissions and I think a LockButton can only be responsible for one permission.