function addSongToPlaylist(song, playlist) {
    if (_config2.default.playlists[playlist] != undefined) {
      _config2.default.playlists[playlist].songs.push(song);

      if (_config2.default.playlists[playlist].shuffle) {
        _config2.default.playlists[playlist].shuffle_list.push(song);
      }

      if (_soundcloud2.default.isSoundCloudURL(song.url)) {
        _soundcloud2.default.resolveIndividualStreamableURL(song.url, playlist, _config2.default.playlists[playlist].songs.length - 1, _config2.default.playlists[playlist].shuffle);
      }

      return _config2.default.playlists[playlist].songs.length - 1;
    } else {
      _debug2.default.writeMessage("Playlist doesn't exist!");
      return null;
    }
  }
Adds a song to a playlist. This will allow Amplitude to play the song in the
playlist

Public Accessor: Amplitude.addSongToPlaylist( song_json, playlist_key )

@access public
@param {object} song 			- JSON representation of a song.
@param {string} playlist		- Playlist we are adding the song to.
@returns {mixed} New index of song in playlist or null if no playlist exists