Make feedback-related strings accurate

Summary:
Prior strings were inaccurate (I was the one who changed it, sorry about that)
and talked about visual feedback for something that was actually about audio
feedback. Adjust strings to be clearer and actually accurate.

Test Plan: {F6927847}

Reviewers: #vdg, nicolasfella, drosca

Reviewed By: nicolasfella

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D22046