Implement full-text search in Converse

[tazjin]

What the title says.

This is implemented using PostgreSQL's support for full-text search by creating a tsvector of several fields of each post and thread in a materialized view and indexing it.

Postgres' plainto_tsquery function is used to convert user input to search queries to be executed against the database.

ts_headline is used to display relevant snippets from search results on the output page.

Known caveats:

• English is hardcoded as the query language for now
• The materialised view needs to be updated after every change of posts, which currently happens at regular intervals - meaning that it is not always guaranteed to be in sync with the posts & threads on a forum
• Search for exact matches is not yet supported

[tazjin]

Functionality is implemented, but the results page looks kinda broken. That'll be for a followup change ...