Qualify the usage of citations

[nemobis]

To improve the OpenLibrary.org wishlist, I wish the citation dataset told me whether a citation is used in a reference/footnote, rather than just part of a list of works in the article about the author or whatever.

A first easy step should be do add a column which notes whether the identifier was inside a "ref" tag. That only requires a regex.

It's a bit harder to tell whether the citation was included in the footnote indirectly, for instance with the shortened footnote templates (example).