Add document collection to Pelican website

[bbockelm]

We've been trying to be meticulous about publishing Pelican-related presentations and keeping a public collection, viewable here:

https://figshare.com/collections/Pelican/6881710

I'd like to have these be embedded in the Pelican website. It seems there's a reasonable set of APIs (e.g., https://docs.figshare.com/old_docs/api/collections/) for Figshare. Let's use the Figshare APIs to render a page at build time.