requested to merge bharadwaj-raju/plasma-workspace:klipper-clear-dont-save-no into master
Previously the "clear clipboard history?" dialog used
KMessageBox::questionYesNo which if "don't ask again" is ticked then saves the answer even if No was answered. Changes it to
KMessageBox::warningContinueCancel which doesn't do that, and is more appropriate for the kind of question we're asking.