Ensure the aggregator drives traffic back to the source repository.

[anjackson]

As I learned at iPres 2022, usage analytics of format repositories are sometimes used to justify the funding that those source registries need. This aggregator caches some of the registry contents, and shows that to the user sometimes, e.g. to show precisely where data comes from. But where possible, users should be directed back to the original source repository rather than using the cached copy. The purpose of this ticket is to review the aggregator and update and/or add links pointing back to the source.