Summary:
Fixes T12623. Adds new modular transactions to Slowvote. Also converts
the `shuffle` column to `bool` for consistency with other boolean-ish columns.
Test Plan:
Create a new vote, modified everything that could be modified from the web UI,
observed expected timeline.
Example timeline: {F4938843}
Example transaction values in DB: {F4938850}
Reviewers: #blessed_reviewers, epriestley
Reviewed By: #blessed_reviewers, epriestley
Subscribers: Korvin, epriestley
Maniphest Tasks: T12623
Differential Revision: https://secure.phabricator.com/D17830
