Display amount of students per assignment (Course view)

[mkdir-washington-edu]

Count the amount of students for every assignment, and display it in the course view.

[mkdir-washington-edu]

In the All Courses view (each row lists a course you're teaching with Hypothesis) we should have a count of all students in the course who have accessed Hypothesis. We will combine this with the total number of students we get from the course roster. So "12/20 participating students".

In the Course View (each row lists an assignment in the current course you're viewing) we should list the number of students who have accessed the assignment.