Handle modifications to courses that are already started by some students

Problem/Motivation

Currently admins / teachers are allowed to modify courses or lessons being a part of courses that are already in progress by some students, breaking existing course / lesson status data that will no longer be up to date.

Proposed resolution

• Issue a warning when editing / deleting a course that has existing in progress / needs evaluation course statuses. Reset those statuses on course update.
• Issue a warning when editing / deleting a lesson that has unfinished lesson statuses. Reset course statuses referenced by those lesson statuses (removing those lesson statuses at the same time).
• Issue a warning when editing a question that has unevaluated answers (teachers can wrongly score those answers if the question changes), in this case a warning should be enough.
• Issue a warning when deleting a question that has unevaluated answers. Reset course statuses for courses having those answers on delete.
• List affected courses in those warnings.