* 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
This commit includes an improved Preferences dialog for KMix.
It also exposes some previously hidden options and features,
some of which experimental (build-time option, off by default).
It also includes some minor UI improvements.
Signed-off-by: Mavridis Philippe <mavridisf@gmail.com>