* XDG-compliant icon names with volume level specification (low, medium, high)
Low-Medium threshold: 33%
Medium-High threshold: 67%
* Improved built-in icon theme with distinct volume levels (according to above)
* Choice between classic KMix icon theme, imrpoved KMix icon theme and system theme.
* New KMixDockWidget::getAvgVolume() method
Gets average volume in %. Code actually comes from KMixDockWidget::setVolumeTip(),
but was put into a separate method to be reused for determination of icon according
to the volume level
Mavridis Philippe