Add side by side browser link for each mapping

**Please do not merge yet - opening this PR for help and review only.**

I think the problem I'm having with testing these is I can't find any real-world examples that meet all of the criteria - `phe_arsac` works for not being live yet, but it doesn't have any AKA domains. I originally wrote the features with BIS as the organisation, but they're still failing. I don't know if it's me, Cucumber, or the data. I've committed the failing tests.

Someone taking a look would be greatly appreciated. :eyes: