R1:b767bd3f2d9d

Move Herald rule querying into HeraldRuleQuery

Summary: Ref T2769. The `HeraldRule` class has some query logic; move it into `HeraldRuleQuery`. Also some minor cleanup.

Test Plan: Ran test console, created a new revision, used `reparse.php --herald`. Verified rules triggered correctly.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2769

Differential Revision: https://secure.phabricator.com/D6689