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
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