Recommend terms by matching research descriptions agains term definitions (using FTS)

[arteymix]

MySQL supports natural language full-text queries: https://dev.mysql.com/doc/refman/8.0/en/fulltext-natural-language.html

Relates to #136 to prepare full-text indices on research interests.

• [ ] add an action to add an individual (or multiple) term to a user profile)
• [ ] review how that would play out with taxon-specific terms
• [ ] display recommended terms below the profile description

[arteymix]

We don't need a full text index on the search query as we cannot use the description column in the match-against syntax.