Fixed downloading of private playlists
This commit fixes the download of private playlist links. The issue was that fetching the playlistAPI using dz.gw.get_playlist_page(id) yields a dict structure that is completely different from the public api call to dz.api.get_playlist(id). Mapping the api with map_user_playlist() from deezer-py fixes the problem. Since deemix expects the creation_date key to be present deezer-py!2 (merged) has to be merged first.
Ideally playlistAPI should be a custom data type since that would mitigate further compatibility issues.