Add Start and Stop Date to Survey Instances

[jonmbake]

Background

Currently, the only way to stop a survey instance from being deployed is to the remove the Survey Instance definition JSON file from the survey_instances directory. Add start and stops date to automatically start/retire a survey instance.

Technical Details

Add start_date and stop_date properties to the Survey Instance definition. Routes should check the current server date against these dates and present the user with a message if they attempt to access the survey when it is outside this date range.