Suggest Phurl URLs on "((..." in Remarkup text areas

Summary: Depends on D19108. Ref T12241. Ref T13077. See D19108. This extends the [[ ... autocompleter to ((... for Phurl URLs.

Test Plan: Typed ((th, got ((thing)) suggested.

Reviewers: avivey

Reviewed By: avivey

Maniphest Tasks: T13077, T12241

Differential Revision: https://secure.phabricator.com/D19109