Broke conversion from logit to fraction into it's own function for reusability.
Added basic structure question-analysis reporting.
Added '% Correct' statistic.
Added 'Answers' statistic-column
Added a basic 'discrimination' statistic.

The definition of this statistic can likely be refined to be more statistically
valid, but this definition should be a useful placeholder for initial evaluation.
Added a placeholder "estimated level" statistic.
Added a single-question report that includes all stats for that question.

This report allows teachers to see the question itself as well as all answers
for it and calculated statistics about the question.
Removed the "Estimated Level" statistic as it was not helpful.
Merge branch 'MOODLE_23_STABLE' into adpq-9-Report-of-question-usage-and-efficacy

Conflicts:
	lang/en/adaptivequiz.php
Coding Style: fixed white-space errors.
Coding Style: Variables must not contain underscores.
Coding Style: Added missing curly braces.
Coding Style: Fixed comment placement.
Coding Style: Inline comments must end in full-stops, exclamation marks, or question marks.
Coding Style: Removed extra white-space.
Coding Style: Lines shouldn't exceed 132 characters
Coding Style: removed commented-out code.
Merge branch 'MOODLE_23_STABLE' into adpq-9-Report-of-question-usage-and-efficacy
Coding Style: Fixed missing white-space found when running phpcs from the command-line.
Merge branch 'MOODLE_23_STABLE' into adpq-9-Report-of-question-usage-and-efficacy

Conflicts:
	lang/en/adaptivequiz.php