Add a preferences-system-splash icon for the Splash Screen KCM
Summary: Add a preferences-system-splash icon for the Splash Screen KCM.
Test Plan:
At 100%:
Reviewers: VDG, ngraham
Reviewed By: VDG, ngraham
Subscribers: ngraham, kde-frameworks-devel
Tags: Frameworks
Differential Revision: https://phabricator.kde.org/D18278
