R1:1c51ed594065

Use TransactionEditor in differential.createcomment

Summary: Ref T2222. Update this callsite; pretty straightforward.

Test Plan: Used Conduit to take actions and saw their effects in Differential.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2222

Differential Revision: https://secure.phabricator.com/D8442