Added elemental playback functionality: can play a single file and show information of it in bottom panel.

TODO FOR NEXT COMMIT:
> show track position and length
> program previous/next buttons, handle stack playback
> program play/pause button
> (maybe this commit) implement progress bar
> implement song context menu

NOT YET IMPLEMENTED:
- albums, artists, playlists and now playing panel
- Windows 7 APIs
- Multimedia key support
- (Possible) Show mini player when using multimedia keys