Hard-code some RIS/BibTeX URL patterns?

[dstillman]

E.g., https://forums.zotero.org/discussion/comment/444847/#Comment_444847 — Primo 2018 uses a URL that ends in /exportris. They should obviously use an appropriate Content-Type, but /exportris isn't going to be anything else, so it seems like we could do this.

If we really wanted it to be scoped to translators, an alternative might be to let translators make a specific function call in detectWeb() to indicate that the current site might trigger a specific URL pattern that should be imported, but that seems overly complicated.