Big big update!

- fixed gray screen update; issue was that MediaCtrl wasn't a child of
the parent panel
- implemented all major functionality; play, pause, stop buttons all
work
- implemented moving slider; slider moves as the song plays and can be
used to jump to any position in the song currently playing (this was a
pain in the ass to implement)
- todo: 'playlist' functionality.
- todo: display some mp3 metadata?