Fixed the issues with adding subgroups and updated the demo fixtures.
Added deadline checking for the front-end (only maintainer can edit endorsed deadlines) and updated the leave group handler.
Added logic to differentiate adding a course from adding a subgroup.
Fixed the modal fields and syles associated with adding subgroups and courses.
Added functionality that prevents users from editing the times of deadlines that are endorsed.
Merge branch 'master' of github.com:NintenJoe/cs411-project