Enforce new muted icon style in all action icons

Summary:
This patch updates the 16px player-volume-muted to be a symlink to the corresponding status icon. It also changes the 24px audio-volume-muted action icons to the new muted symbol introduced in D17220: Improve symbolism for off and muted status icon.

It also adjust the opacity of the inactive sound waves in the 24px audio-volume-low and audio-volume-medium icons to 0.25 to match the Breeze Plasma theme.

Reviewers: VDG, ngraham, rooty

Reviewed By: VDG, ngraham, rooty

Subscribers: ngraham, kde-frameworks-devel

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D19307