Give Herald rules a standard "Hnnn" object name

Summary: Allow Herald rules to be referred to with `H123`, etc., like other object types are. Herald rules now have proper PHIDs and an increasingly prominent role in triggering application actions. Although I suspect users will rarely use `H123` in Remarkup to mention rules, this can simplify some of the interfaces which relate objects across systems.

Test Plan: Looked at various interfaces and saw `H123` names. Mentioned `H123` in remarkup.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D7786