Added Changes to Audio Player and File Chooser

Added specific directory to open for Open File dialogue window so I
don't have to navigate to the directory where my .wav files are every
time I want to choose a file (very handy). Added a file filter to the
file chooser so only .wav files will display in the Open File dialogue
window. Fixed a bug where if there user hit the play button multiple
times the audio player would instantiate that many audio streams
resulting in that many songs being played. Added the ability to stop a
song while it is currently being played.