Make KCM look more like applet
Summary: I was looking through changes in plasma-pa and noticed, that the KCM looks very different in contrast to the applet.
Test Plan:
Checked for mute button function on all occasions (sinks, sources, applications playing, applications recording). Checked if volume slider works as expected.
Reviewers: Plasma, VDG, ngraham, GB_2
Reviewed By: VDG, ngraham, GB_2
Subscribers: drosca, ngraham, davidedmundson, GB_2, Plasma, plasma-devel, VDG
Differential Revision: https://phabricator.kde.org/D24161