Change default Klipper behavior to accept images

Summary:
Change the default Klipper behavior in order for https://phabricator.kde.org/D19715 to work.

Klipper will save images to clipboard, but unless Ignore Images is unchecked in the options, it won't save them to clipboard history.

CCBUG: 393708

Reviewers: Plasma: Workspaces, davidedmundson

Reviewed By: Plasma: Workspaces, davidedmundson

Subscribers: ngraham, davidedmundson, plasma-devel, Plasma: Workspaces

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D19852