public Track CreateTrack(long playlistId, Track track)
{
var playlist = ReadPlaylist(playlistId);
if (playlist == null) return null;
var playlistTrack = new PlaylistTrack {Track = track};
if(playlist.PlaylistTracks == null) playlist.PlaylistTracks = new Collection<PlaylistTrack>();
playlist.PlaylistTracks.Add(playlistTrack);
context.SaveChanges();
return playlistTrack.Track;
}