Add Room typeahead for Conpherence Search

Summary: Ref T3165. Builds an ngram table for Conpherence Room titles, allowing a tokenizer for searching a subset of rooms.

Test Plan: Say Gabbert in two different rooms, search all, see two rooms returned. Search specific room, see specific result.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Maniphest Tasks: T3165

Differential Revision: https://secure.phabricator.com/D16692