[NPG] Attach supplementary info and some useful links

Behavior can be controlled by extensions.zotero.translators.attachSupplementary and supplementaryAsLink

This turned out to be quite a PITA, but I think it's rather useful to have these attachments as files or links. Should be much easier to do this for more focused translators.

We can add more links like GEO, but I'd need to see some examples to implement them. Perhaps I'll get to it before this is merged.

What do you guys think?