* Support for old non-standard cron for quiz reports dropped. (Standard
cron support was added in 2.2
* Cron support added for qbehaviour, qformat and quizacces plugins.
* qtypes were already supported in the standard way.
Previously, for the overall grade, we averaged the final marks for each
student; while for the individual question grades, we averaged all
grades.
The report now works consistently on the principle that the averages
should include exactly what is currenlty being shown in the report. This
is more logical, and so should be easier for users to understand.
If you want to see the averages that are currently shown (e.g. just the
average of each student's highers grade) then the report options let you
do that.
This achieves a massive clean-up. It simplifies comples code in a number
of places. It allows some methods and functions to be moved to a more
appropriate home (for example cannot_review_message to the quiz class).
It moves more logic out of the renderer.