R1:bf9bc885b764

Enable notifications by default

Summary: I think we've sorted out enough of the problems with these to turn them on for everyone. The real-time component remains configuration-dependent.

Test Plan: Turned off "notification.enabled", still saw notifications.

Reviewers: btrahan, chad

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D4120