added new features, renamed file

- Added new feature: when a song in the playlist is double-clicked, the
song will automatically start playing. NOTE: this functionality relies
on the EVT_MEDIA_LOADED event, and for some reason the DIRECTSHOW
backend won't fire it properly. This issue has been noted in the wx bug
tracker. Changed the backend to WMP10 for the time being.

- added a 'delete from playlist' button, allowing users to remove items
added to the playlist.