kcm/qml: Show status when adding or changing a printer device

Noticed when testing with users on slow machines, sometimes saving changes to a printer or adding a new printer can take up to 15 seconds. Not sure why, sometimes the same save happens instantly.

There are comments that CUPS is doing ppd creation and other housekeeping things that can block. Somewhat unclear, but either way, let's at least keep the user informed.

Also small fix for Banner reset and disable padding for Banners in headings See commits