Support Spotify

[ErikBjare]

Was talking with @karvla about Spotify support (and how I thought it'd be difficult) but then he told me that Spotify has these "top artists" and "top tracks" which you can access. "Huh", I thought, and quickly checked if you could get that info through their API, and you could!

So this is on the TODO now, not sure how API authentication and all that would work but at least it seems to be possible as opposed to what we previously thought.