Additional weighted review times

Problem/Motivation

We currently have two feedback times, "after the question" and "after the quiz". We should be able to add additional times to show more conditional feedback.

For example you may not want the user to see correct answers unless they have passed the quiz. Or, only show certain feedbacks like peer comparisons for a length of time. Or, only showing results X days after the quiz, after the learner has reviewed it with the instructor.

Proposed resolution

The feedback options are currently alterable by modules, so the feedback times should be as well.

For each feedback time, use rules to let the conditions be configurable.

Remaining tasks

- Add quiz_get_feedback_times() that mirrors quiz_get_feedback_options()
- Delegate criteria to Rules
- Tests
- API Documentation

User interface changes

- None

API changes

- Added hook_quiz_feedback_times()
- Added hook_quiz_feedback_times_alter(&$feedback_times)
- Added quiz_get_feedback_times()
- Improve hook_quiz_feedback_options()
- Improve hook_quiz_feedback_options_alter(&$feedback_options)
- Improve quiz_get_feedback_options()

Data model changes

None