Add artists statistics

[matthias4217]

Most played artist and stuff like this

[Ardhanaariishvara]

Very hard with the current implementation that has no uniformisation.

[matthias4217]

Indeed, when getting information through youtube-dl, it sometimes get the correct artist, and sometimes it's just the channel which uploaded the music. I was thinking more about "not accurate" statistics. However, as it wouldn't be great, it's definitely not a priority.