created an hybrid property in CriteriaAndCourses to tell us whether

the criteria is being used by any questions in the course. I used this
attribute to hide the Drop link for dropping criteria from courses.
added group filter in evaluation results and question page

- In the evaluation results page, users can select a group, and all the
comments made by students in the selected group will be shown
- in the question view page, if a group is selected, all the answers
submitted by students in the group will be shown.
- the sorting by score feature is also implemented.