Disable Herald more aggressively when it's turned off for a repository

Summary:
Currently, disabling Herald only disables feed, notifications and email. Historically, audits didn't really create external effects so it made sense for Herald to only partially disable itself.

With the advent of Harbormaster/Build Plans, it makes more sense for Herald to just stop doing anything. When this option is disabled, stop all audit/build/publish/feed/email actions for the repository.

Test Plan: Ran `scripts/repository/reparse.php --herald`, etc.

Reviewers: dctrwatson, btrahan

Reviewed By: btrahan

Subscribers: aran, epriestley

Differential Revision: https://secure.phabricator.com/D8509