Support for multiple rectangle hitboxes in imageresponse

Fix imageresponse in Firefox

putting vsepr static image files where vsepr js can find them. TODO: reogranize after proper input type static file storage is sorted out.

Permit collapsibles in capa detailed solution

Add an end date to courses.

- needed for cert generation (and later lots of other things)

Vik/add instrumentation

Vik/add instrumentation

Increase the limit of files that can be uploaded by a student

Add some extra console commands for handling user permissions

Make problemset render as a sequential, not a vertical.