Typeahead is broken in v4.x

[Jon Couldridge]

Typeahead is broken throughout the site.

• The public search input typeahead returns no results, despite the elastic search query being successful (and returning matches)
• The Disease Status typeahead when selecting a term for creating a Collection returns incomplete and apparently inconsistent results, and is affected by different text case.

Both the above should be consistent and case-insensitive partial term matches.

Public search should also use other terms as synonyms.