Covid slider

[Dmitry Kobak]

Ben, I'm not sure how to do double filtering: I want the Covid slider only show Covid papers, for this we need to filter based on covid_label and also based on date. Can you help me with the syntax? I left a comment it in the markdown file.

[Benjamin Schmidt]

Here's the fix, now published upstream.

6b0ed53

Note that only filter2 is allowed--there's no filter3. The foreground aesthetic can be equivalent to a third filter, though, if we ever need one.