"Visited" status on voter is updated

[BenGalewsky]

As a volunteer I want to see which voters I've visited so I can visit new voters.

Acceptance Criteria

1. Voter list has a column indicating whether the voter has been visited
2. Volunteer can filter the list to show only un-visitied voters
3. Entering responses for a voter sets their visited state to true
4. Volunteers can enter a "no response" response for voters who did not wish to talk