Revert "Revert "LEARNER-1510 Add unenrollment reason survey""

lms/djangoapps/courseware/features/registration.feature

lms/static/js/dashboard/legacy.js

lms/static/js/learner_dashboard/unenrollment_factory.js

lms/static/js/learner_dashboard/views/unenroll_view.js

lms/static/js/spec/learner_dashboard/unenroll_view_spec.js

lms/static/lms/js/build.js

lms/static/lms/js/spec/main.js

lms/static/sass/multicourse/_dashboard.scss

lms/templates/dashboard.html

lms/templates/dashboard/_dashboard_course_listing.html

lms/templates/dashboard/_reason_survey.html