Add fulltext search to Maniphest custom query screen.

Summary: Allow fulltext search on custom query screen using the same fulltext search as the search page.

Test Plan: Enter search terms - with and without additional filters - see the expected results. Don't enter search terms - with or without additional filters - and see the expected results.

Reviewers: epriestley

CC: aran, Korvin

Maniphest Tasks: T1305

Differential Revision: https://secure.phabricator.com/D2763