as well as for first or all attempts.
This commit drops a database table and then recreates it. This is in
order to be able to have some new columns in the table be NOT NULL with
no default value, which would not be possible if I added fields to an
existing table.
The quiz_statistics table is used for caching calculated values only
and thus we can safely drop it and recreate it.
quiz_question_statistics_stats renamed to question_statistics_calculator
separate class question_statistics used to store calculated stats
and api changed, also code generally cleaned up.
James Pratt