Add implicit CC rules to ApplicationTransactions

Summary: When you make a comment on an object (or take certain other actions), we want to automatically CC you. Build this into ApplicationTransactions since it's a common behavior shared across multiple apps. Fixes T2215.

Test Plan: Made a comment on a macro, got cc'd.

Reviewers: chad

Reviewed By: chad

CC: aran

Maniphest Tasks: T2215

Differential Revision: https://secure.phabricator.com/D5019