Features to accommodate the late work policy

[christianp]

We've done some thinking about how we can follow the school's late work policy.
Students are allowed to submit work up to a week after the deadline, with a penalty based on the number of days late.

Our central systems should be in charge of determining whether and how much of a late penalty to apply, but in Numbas LTI it should be possible for students to opt in to continuing to work on attempts after the due date, but within a defined availability window.

Tasks:

• Allow students to re-open their own attempts while the resource is available. (Enabled by a resource setting, default on.)
• Always allow students to open their attempts in review mode with no feedback.
• Add a "due date" field to resources. Any submissions after this time are considered "late".
• When re-marking attempts, use the time of the student's last SCORM element as the time for reporting scores.
• For attempts in progress when the due date comes, kick the student out and back to the attempts listing. They can choose to re-open the attempt and go back in, acknowledging that their work will be marked late, until the resource becomes unavailable.