Ability to export data dumps for a course/workout/exercise/student

[ayaankazerouni]

Initial request was to include an option for "extra info" when downloading grades from the roster page, for example if the instructor wants to know how many attempts were required to arrive at the current grade.

But what we really want is some kind of interface in which instructors can generate and download reports for:

• an entire course section
• the work from all students for a given workout offering or exercise
• all attempts from a single student on a workout offering or exercise
• information for individual test cases in an exercises, e.g., to see if many students were failing particular test cases

This needs some thought to figure out what information instructors would find useful to export, the UI, etc.