Updated comment to reflect current operation of the code.

The SQL statement was changed in cdc19a8b8589030632dc90259f0f0750b18cb7e2 but the
in-line comment wasn't updated.
Issue #15: Now shows the date of the best attempt in the main report.

Teachers can now view and order the report based on attempt finish time.
For placement exams this is important as staff need to be able to check for
new submissions.

This fixes #15.
The best score shown in the main report now links to its corresponding attempt review.

This cuts down on the number of clicks necessary to review attempts.