Make a handful of minor Slowvote behaviors more consistent with other applications

Summary:
Ref T12685.

• Better icon/color/label consistency.
• Make "0" a valid response.
• Fix a bug where creating a poll with Quicksand enabled led to bad times (form submitted back to the search screen).

Test Plan:

Reviewers: chad, amckinley

Reviewed By: chad

Maniphest Tasks: T12685

Differential Revision: https://secure.phabricator.com/D17878