Add mute button with dynamic icon to MPRIS volume control

Summary:
The icon changes depending on the slider value and clicking it
will switch the volume between 0 and 100

Reviewers: KDE Connect, nicolasfella

Reviewed By: KDE Connect, nicolasfella

Subscribers: apol, broulik, albertvaka, nicolasfella, kdeconnect

Tags: KDE Connect

Differential Revision: https://phabricator.kde.org/D16962