Songkick integration

It'd be great to have some form of integration with [Songkick](https://www.songkick.com) which uploaded a list of your artists to their website, allowing you to find out upcoming concerts for music you are interested in.

They seem to have an [API](https://www.songkick.com/developer) but you have to [request a key](https://www.songkick.com/api_key_requests/new) and it doesn't seem to provide any functionality for actually [tracking artists](https://www.songkick.com/developer/trackings).

I took a quick look at the request made when tracking an artist, and it simply seems to be a POST request to `https://www.songkick.com/trackings` with some parameters (only showing required ones here);

```
authenticity_token: [TOKEN FROM ARTIST PAGE]
relationship_type: concerts
subject_id: [ARTIST ID]
subject_type: Artist
```

And to untrack, it's just the same request but to `https://www.songkick.com/trackings/untrack` instead.

We can use their official API to fetch the ID of an artist (the `subject_id` value), but we'd need to scrape that artist's page to get the token for the request.