Create anonymous statistics report

[hgeorgsch]

This can be done off-line, so it is not critical at this stage, but for the sake of usability and possibly statutory requirements, it would be better if the user could select an anonymous report, where all personal information is removed and only a pseudonym given (allowing attempts to be grouped by user).

The numeric user ID may not be quite sufficient. Ideally it should not be possible to link users between reports.