Cleanup audio feature extraction code

Refactor sonic annotator code into new class and improve flexibility.

Add new Audio Feature class that contains code to extract both onsets
and segments from an audio file using the sonic annotator class.

Clear colour of screen now changes to a random colour based on the current
segment's identifier.

Remove QMVampWrapper class as it's functionality has been refactored
out into the AudioFeatures and SonicAnnotatorWrapper classes.

Added qmsegments.n3 plugin descriptor file for segments. May need to tweak
the values a bit, possibly increase min. segment duration and decrease
maximu segments?