Auto-copy shared image link to clipboard

Summary:
Whenever an image is shared and a link is provided, the link is automatically copied to the clipboard.

We also rename the Copy save location checkbox to prevent user confusion with this new feature (and also to better reflect what the Copy save location feature actually does).

FEATURE: 392722
FIXED-IN 18.08.0

Test Plan:
Shared an image via Imgur. The link immediately appeared at the top of Klipper's history.

Reviewers: Spectacle, KDE Applications, rkflx

Reviewed By: Spectacle, rkflx

Subscribers: kde-doc-english, rkflx

Tags: Documentation

Differential Revision: https://phabricator.kde.org/D13493