Student should get teacher feedback

When a student submits an exercise or workbook entry, they should be able to get back feedback from the teacher. This could be a list of items they got correct and also comments. This feedback should come back to them in the same form as they submitted, i.e., they are still inside the reading system.

The issue names no files, tests, or entry points, so begin by clarifying the submission and feedback flow with the project maintainers. Done should be defined as students receiving correctness information and teacher comments within the reading system, in the same form used for submission.

Written by the indexing model from the issue text.