[Applet]Fix device label problems

Summary:
Limit label maximum width, to avoid breaking UI.
Change label to use plasma components 3, for theme color compatibility.
Use of implicit sizes, to avoid binding loops.

BUG: 417074
BUG: 417106

Test Plan:
Use applet outside of systemtray and limit it's width.
If device description is not long enough, enable in the configuration
"Add virtual output device for simultaneous output on all local sound cars".
Before: Hamburger menu moves to the right, and there is no eliding.
After: Proper display.

Reviewers: Plasma, VDG, drosca, ngraham, davidedmundson

Reviewed By: VDG, ngraham

Subscribers: cfeck, plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D27117