Our draft/ready publication model (which displays both versions using the same URL, unfortunately) causes a subtle bug here due to caching.  Since caching is keyed on URL, an instructor in "Edit" mode can try to fetch the right nav from this view, which because of the mode="ready" filter in `get_upcoming_exams()` will return no exams.  Then, this blank right nav will get cached and be served to all users, including students in the "ready" mode.   (I tripped across this during testing)

I think the solution here is to get `ready_course` from `common_page_data` and use that in `get_upcoming_exams`.