Implement number of retries for a lesson / course (exams)

Problem/Motivation

Still not sure if a number will be needed vs retries allowed / not allowed and if this should be on a course or lesson level (lesson level would make this more flexible but would require additional parameters and logic).

Proposed resolution

• Add number of takes data item in lesson LMS Reference field (0 - unlimited, 1 - only one (exam mode)).
• Add int attempt no field in lesson status to keep track of that.
• Add a lock field in course status that disallows a user from retrying a course when locked, it could be an int with value 0 representing an unlocked course and everything else being flags representing various lock reasons.
• On course status recalculate, check if any mandatory lesson status reached max retries count, if so, lock the course.

This should allow all display to be cacheable by adding a course status only as a dependency.

Remaining tasks

Implement

User interface changes

Additional data parameter in LMS Reference on course lessons.

API changes