Initial Implementation of Music Visualization using VSXu.

For more information on VSXu: 
visit : www.vsxu.com
https://github.com/vovoid/vsxu 

Currently the Visualizer Widget is added only if VSXu is found at the build time.

TODO: Think of a clean way to add advanced visualization controls like next visual , previous visual etc.. 
TODO: Add more rigorous checks about the OpenGL context before enabling the VisualizerWidget. Currently the worst machines this has been tested on are: a 10 year old desktop with ATI Radeon Card with OpenGL version 2.0, a 6 Year old laptop with Intel GMA 945 card with OpenGL version 1.4(fixes for this are in VSXu master), a recent laptop with NVIDIA GeForce 8400M card.