user can see assignments in their cohorts, admin user can create assignments from admin panel that automatically link to main cohort; admin user can select main or  not main when associating with a new cohort (though this will currently only create a new enrollment regardless of whether that enrollment already exists) and student user can just associate with new cohort and it auto selects whether its main or not (though maybe this needs to be just like admin for now?) && main cohort is a boolean value in enrollments table