R1:aa2e6d1e5a4e

Make most slowvote fields edit transactionally

Summary: No support for responses yet, since they're more complicated, but put everything else on the transactions plan. This also prepares polls for editability, shortly.

Test Plan: {F50205}

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D6460