Fix crash in list_playlists()

Google Music allows multiple user playlists with the same name,
so the 'user' dictionary will map onto lists of ids.

There is currently no support for retrieving automatically-created
instant mixes, so removing "auto".

Please see:
http://unofficial-google-music-api.readthedocs.org/en/latest/reference/api.html#gmusicapi.api.Api.get_all_playlist_ids
and
https://github.com/simon-weber/Unofficial-Google-Music-API/issues/67
Merge pull request #7 from reggna/pr-2

Fix crash in list_playlists()