With the addition of the peak volume indicator, themes may wish to change
these colors but there was no way to do so. This change updates the
VolumeControl widget to allow a stylesheet to adjust all possible colors
for the volume bar. In addtion, the Rachni theme is updated to demonstrate
this new capability.
When the OBS signal is triggered for these widgets, the invokeMethod
could cause the thread to stall, which could make it wait much longer
than necessary to output audio data. When that happens, it causes audio
monitoring to get backed up and get unnecessarily delayed, as well as
cause general audio buffering in libobs to increase unnecessarily.
A simple fix both in terms of preventing that stall and improving UI
performance is to not call invokeMethod to update the widget each time,
and then instead have those widgets update themselves via a timer at a
specific interval.
