R1:ea52bcbcd651

Migrate Slowvote comments to ApplicationTransactions

Summary:
Move comments from the old table to ApplicationTransactions. Patch dances around which objects it uses since I intend to delete the comment table.

NOTE: This temporarily disables comment writes. I'll restore them shortly.

Test Plan: {F50166}

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D6454