Add survey to the homepage
Login required to take the survey
Allow users to take a survey. Important notes:
* modify survey_params in the survey controller to accept survey responses attributes
* surveys have many survey responses through survey questions
* survey questions accept nested attributes for survey responses
* in take_survey action, build/initialize each survey response to the user id
* we reject blank questions (to facilitate creation of the survey with questions) so be sure to include question in the form for survey responses, otherwise rails will reject them
Add links to login on signup page and vice versa
Dashboard to view survey answers
Possible responses should be radio buttons
Adding surveys to navbar for admins
Populate flash error message when invalid login