Investigate use of tippy.js for term hover

[jzohrab]

We have a few issues for the term hover (e.g. #236, #355, #357), all having to do with the amount of info shown on the hover.

Hovering is added by $('#thetext').tooltip({ in static/js/lute.js, using jquery. It might be better to try tippy, as suggested by @webofpies in #236.

I did some initial hacking in branch wip_issue_360_tippy_for_term_popup_interactions pushed to this repo. A demo:

As shown, the initial popup has some child terms, which are themselves tippies. To see the child term tippy, you click on the child term (this seemed more stable than hover). The child terms should have some kind of hover links or similar to show that they should be clicked. You can click on a tippy further up the chain, and everything else is hidden.

Scope of work for further investigation:

• all of the tippy stuff should go in lute/static/vendor/
• see if there's a minified version of tippy and its css -- I don't think we need all of it. https://atomiks.github.io/tippyjs/v6/getting-started/#2-cdn has some production URLs, could commit those as they're minified etc.
• proof-of-concept to show multiple tippies created off of single one
• try replace ajax of proof-of-concept demo with call to the endpoint, and initialize the child terms with their own tippies
• try using the tippy in place of the existing jquery tooltip
• ensure it works on mobile!!!
• figure out themes - eg dark etc, they should all somehow be applied to the tooltip. Maybe use headless tippy to ensure all themes are good as-is, though that seems like a hassle.
• only use this for the term popup, no messages etc. i.e. should only be related to $('#thetext').tooltip({ in lute.js.