R1:355142fcbf23

Reduce code duplication on comment editing UI

Summary: Ref T2009. This has two more copies of the scaffolding.

Test Plan: Created, edited, deleted, replied to inline comments.

Reviewers: btrahan, chad

Reviewed By: chad

Subscribers: epriestley

Maniphest Tasks: T2009

Differential Revision: https://secure.phabricator.com/D12018