beef the user form. fixes #271, fixes #71

add read-only fields "ccing users" "represented users", and "courses contributing to", add writable "Courses partricipating in" and remove "represented users".
rename all enroll* zu participant*
add field is_graded to courses. fixes #284
small refactoring around the SelectCourseForm
sublime-ignore the submodules
fix the faq section form. it was not possible to add a question, and the leave.js popup appeared when saving.
update jquery.ui.formset, remove all our modifications to it. fixes #416, fixes 417
ContributorFormSet: don't validate contributions marked for deletion. fixes #415