Deezer importer: Issues

[MaxEtMoritz]

Hi, Thank you for your work in building all these import scripts.

Today while using the Deezer importer i came across two issues:

1. The importer only imports the first 25 tracks of an album, not the complete one. Probably a pagination issue?
2. Only the main artist is imported, additional artists are missing.

I looked at what Deezer returns from the API, and to resolve 1., a check if nb_tracks is greater than the length of the tracks array needs to be done. if this is the case, the next tracks need to be requested from https://api.deezer.com/album/<album_id>/tracks?index=<track array length> (by the way, this track list also lists track ISRCs that could be submitted to MB).

For 2., not even the dedicated track list includes all artists (unless there's a parameter that can be set to include those. Don't have a deezer account that would be necessary to check the official api docs). Requesting each individual track would include those artists.

Unfortunately i do not have the time to assemble a PR that resolves 1. since i'm going on vacation tomorrow.