In case an exercise is listed in more than one assignment, we make sure we
only list the exercise once per assignment.
Removed unnecessary code.
Merge branch 'master' of https://github.com/OpenDSA/OpenDSA-server

Conflicts:
	ODSA-django/opendsa/exercises.py
Merge branch 'master' of https://github.com/OpenDSA/OpenDSA-server

Conflicts:
	ODSA-django/opendsa/views.py
Merge branch 'master' of https://github.com/OpenDSA/OpenDSA-server
Merge branch 'master' of https://github.com/OpenDSA/OpenDSA-server
Merge branch 'master' of https://github.com/OpenDSA/OpenDSA-server
Merge branch 'master' of https://github.com/OpenDSA/OpenDSA-server
Merge branch 'master' of https://github.com/OpenDSA/OpenDSA-server
Merge branch 'master' of https://github.com/OpenDSA/OpenDSA-server
Merge branch 'master' of https://github.com/OpenDSA/OpenDSA-server
Merge branch 'master' of https://github.com/OpenDSA/OpenDSA-server
Fixed duplicate exercises in teacher view class spreadsheet.