Use PhutilBugtraqParser in Phabricator

Summary: Fixes T3840. Depends on D7021. See task for discussion. Also improved some config/help stuff.

Test Plan: See screenshot.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T3840

Differential Revision: https://secure.phabricator.com/D7022