Better multimedia related icons

Summary:
Improves the screen background gradient in the multimedia related icons to make them look better.

Test Plan: Open cuttlefish and search for applications-multimedia

Reviewers: Breeze, VDG, ngraham

Reviewed By: Breeze, VDG, ngraham

Subscribers: ngraham, rooty, VDG, kde-frameworks-devel, Breeze

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D17919