Add an audio analyzer visualization applet.

The analyzer code itself is lifted from Amarok 1.x and then adapted for our
needs. The architecture allows adding multiple different visualizations, both
2d (QPainter) and 3d (OpenGL). Currently I have only implemented the
"BlockAnalyzer" which is rendered with QPainter, so it's guaranteed to work
everywhere.

Caveat:
Due to limitations in Phonon-VLC (and libVLC), the analyzer currently
only works with Phonon-GStreamer.