Added radomized music. Can be changed if we don't like Vivaldi.

NB: In order for it to work, you will need to copy gdd2xna\gdd2xna\gdd2xna\MusicInfo.txt to gdd2xna\gdd2xna\gdd2xna\bin\x86\Debug\MusicInfo.txt

Sourcetree can't recognise files in the bin folder for whatever reason.