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