[WIP] Citations page for Tax-Calculator

[chusloj]

This PR introduces one way to display project citations discussed in #186. Here, just for example's sake, a new citations.html page has been created that lists only OG-USA and then directs to the citations page on their Jupyter Book documentation site.

I'm thinking the following:

1. Scrape the whole .bib file of citations for Tax-Calculator from Zotero using something similar to the following:

curl -H 'Zotero-API-Version: 2' -H 'Zotero-API-Key: <key>' 'https://api.zotero.org/users/6708260/items?format=bibtex'

2. Use Launchd, the same program that @Peter-Metz uses to update the PSL_catalog.json file daily, to scrape this .bib file regularly (probably daily) and push it to the Tax-Calculator Jupyter Book docs – The .bib file renders automatically as a page with formatted citations which @jdebacker shows in Aggregate project citations from maintainer-curated documents #186.
3. The GH action which builds the JB docs daily will take care of the rest.

If this doesn't sit well, a new "citations" link under each project on the catalog page can be added which links to that project's citations within their Jupyter Book docs.

@MattHJensen @Peter-Metz

[chusloj]

Closing as I think this is better off as reply to #186.