Support relative URL addressing in Taxon Links

This request will only be meaningful to site curators.

When creating a taxon link, specifying a URL internal to iNaturalist is currently not feasible, because it will only work if the user is signed in to the same domain contained in the URL, and not any of the other international portals. Being able to specify a relative URL would solve this limitation.

One potential use case mentioned here and the posts immediately following.