Disable search filters

[kmcelwee]

Use CSS to disable things that are no longer functional:

cursor: not-allowed;
pointer-events: none;

Let's keep the drop-downs functional but disable the inputs and the clear selection.

Should be fine to disable form labels and inputs pretty broadly without worrying about filtering too specifically.

• [x] Grey out or lower opacity on form fields — suggest using opacity or rgba/lighter gray color if we want to limit to text (we don't want the drop-down backgrounds to be partially transparent so text may be easier)
• [x] Disable all form inputs (possible exception: search within author filter could be kept active)
• [x] Disable site search bar
• ~Remove clear all~ (no need to remove this, it links to the search with no filters and works correctly)
• [x] Disable "clear selection" on filter drop-downs
• [x] Disable non-default sort options
• ~Deactivate author and reference type links in search results~ (no need to disable, these have been archived)

[rlskoeser]

I think this list is shorter than we thought initially since we're not doing a static site — the browsertrix crawl does capture search filters that are generated from links (like annotation types), so we should not disable them. Ideally, we set the form fields disabled but show the status of the filters or sort options that are active in the archived page. If there's a tidy way to collapse it if no filters are set, that would be nice; if not, I'm inclined to leave it visible always.

[rlskoeser]

completed in https://github.com/Princeton-CDH/derridas-margins-archive/pull/6