Save image to clipboard if --nonotify is used
Summary: BUG: 411263
Test Plan: run spectacle with --nonotify
Reviewers: Spectacle, davidre, ngraham
Reviewed By: Spectacle, davidre, ngraham
Subscribers: ngraham, Spectacle
Tags: Spectacle
Differential Revision: https://phabricator.kde.org/D23723