An updated implementation of the Visualizer, in a clean commit as requested.

This commit should be enable tomahawk to use a basic music visualizer using VSXu 0.3.1.

The visualizer will be silently disabled on machines without an OpenGL backend or when using Phonon with an incompatible audio data backend. (phonon-vlc with libvlc < 2.1 :P )

The visualizer also deactivates itself when it is not being shown, so no CPU resources are wasted when one doesn't use the visualizer.

The whole system "just works". 

:D