Implement mouse wheel for sliders

Summary:
Enable seek and volume control when hovering the sliders in the MediaPlayerControl.
Seek value is hardcoded to 10 seconds, while volume is controlled in steps of 5.

BUG: 408704

Reviewers: mgallien, ngraham

Reviewed By: ngraham

Tags: Elisa

Differential Revision: https://phabricator.kde.org/D22332