disable edit and update past deadline (homework document)  in the controller instead of in model. This is because we need to check for current_user (i.e. grader can still edit), and current_user is not available in the model
fix jquery date picker does not load right away, need refresh (issue: jquery.turbolink, change in Gemfile and application.js). Fix meeting index, minor. Fix submit date using datepicker text field (must use strptime in meeting controller)