add 'order' field to contributions and add migrations
sort contributions in course_forms for staff and contributors and in student_vote
fix test
change tolerance for sortable
prevent "add another" from moving
enable automatic checking/unchecking of responsible and edit checkboxes also for newly added table rows
prevent deleting responsible contributor
refactor student/views.py::vote. make the ordering of contributors explicit.
make the results respect the contribution ordering
Merge pull request #413 from janno42/order_contributors

Order contributors
fix KeyError in message when fully reviewing course