R1:42c0dd2b8e1b

Add mail/feed to Slowvote

Summary: Adds mailkeys, basic structure for publishing to feed, sending mail.

Test Plan: New Poll, vote, comment, etc.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D13749