Integrate subscriptions with ApplicationTransactions

Summary: Fixes T2214. For objects which support ApplicationTransaction, use ApplicationTransactions to apply subscription action changes. Principally, this makes clicking "Subscribe" / "Unsubscribe" appear correctly in the transaction log.

Test Plan: Clicked "Subscribe" and "Unsubscribe" a on Macros and Mocks.

Reviewers: chad

Reviewed By: chad

CC: aran

Maniphest Tasks: T2214

Differential Revision: https://secure.phabricator.com/D4986