Modularize HeraldRule transactions

Summary:
Ref T13249. See PHI1115. I initially wanted to make bin/policy unlock --owner <user> H123 work to transfer ownership of a Herald rule, although I'm no longer really sure this makes much sense.

In any case, this makes things a little better and more modern.

I removed the storage table for rule comments. Adding comments to Herald rules doesn't work and probably doesn't make much sense.

Test Plan: Created and edited Herald rules, grepped for all the transaction type constants.

Reviewers: amckinley

Reviewed By: amckinley

Subscribers: PHID-OPKG-gm6ozazyms6q6i22gyam

Maniphest Tasks: T13249

Differential Revision: https://secure.phabricator.com/D20258