create a GroupingsController #5770
Description
The GroupsController is acting like a controller for both group and grouping models. We should separate out the groupings routes into their own controller:
- repo_browser
- downloads
- valid_grouping
- invalid_grouping
- assign_scans
- assign_student_and_next
- accept_invitation
- decline_invitation
- destroy
Also there are the following routes in the ResultsController that should be moved to either the GroupingsController or TagsController:
- add_tag
- remove_tag