Restore comments on Ponder answers

Summary:
Ref T3373. This is still pretty messy:

• The JS bugs out a bit with multiple primary object PHIDs on a single page. I'll fix this in a followup.
• The comment form itself is enormous, I'll restore some show/hide stuff in a followup.

Test Plan: Added answer comments in Ponder.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T3373

Differential Revision: https://secure.phabricator.com/D6608