Trivial typography improvement

Use an em dash instead of -- in documentation.
GtkRadioButton: Allow setting group more than once

It turns out that GtkBuilder will sometimes set a property
twice. Normally, this is harmless, but for GtkRadioButton:group,
it triggered a critical. Remove that.
Printing: Make the print dialog look better with bottom buttons

With buttons at the bottom, things were not looking good here:
no spacing, and a gray background. Add spacing, and put the buttons
on the white background.
Updated Norwegian bokmål translation.