Expose album URLs

[SilasPeters]

It would be cool, especially when being able to view older activities, to go to the activity's album straight from the activity page on koala. However, this requires koala to know the URL.

1. We could make the URL's deterministic, so that it's URL would be chroma.svsticky.nl/album/{activity ID}
2. Koala can retrieve an albums URL be giving the activity ID

In both cases the activity ID must be associated with the album.

Whether we will use it or not, it would be nice for future purposes to be able to get an album's url

[TobiasDeBruijn]

I like the idea, though I'd go about it a different way.

1. When creating an album, add a field for Koala's activity ID
2. Add an API endpoint to resolve a Koala activity ID to a Chroma album ID
3. Koala can now link to the Chroma album.

Alternatively, with a new activity system, we can link to the album directly in the activity system. This approach I think is better.