Merge pull request #165 from codeforamerica/expand-message-test-coverage

Expand test coverage for messages
Rename Subject to Location.
Rename FeedbackInput to Answer
Add Location#has_voice_messages? and #has_numerical_responses?
Use Location#has_numerical_responses? in LocationController
Add NotificationSubscription.confirmed/.with_new_answers/#newest_ansewrs
Associate Answer with NotificationSubscription
Refactor Notifier