Feature Request: Add support for import / export of playlist files

When exporting a playlist, we should have the option to export it as an m3u or something. Same thing with importing: we should be able to import playlist files (and not just the audio). This would be useful for people who have large playlists and want to sync between the phone and the computer. Instead of manually ordering the playlist so it is identical to the computer, there ought to be a way to do so by sending a file.