Improve symbolism for off and muted status icon

BUG: 398975
FIXED-IN: 5.54

Use a strikethrough version of a neutral icon for *-off icons and a red circle
with a diagonal line for *-muted icons. Also add 22px audio-{on,off,ready}
while we're at it as well as reduce opacity of inactive sound waves to match
the Breeze Plasma theme.

Differential Revision: https://phabricator.kde.org/D17220