Respect phriction.enabled in config

Summary: Eventually we'll have a real "uninstall" sort of thing, but until we do we should keep respecting this flag.

Test Plan: Disabled the flag, saw Phriction vanish from the application list.

Reviewers: btrahan, vrana

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D3724