Tools to delete data from admin interface

[christianp]

Institutions might have data retention policies which require data to be deleted after a set period of time, or might just want to tidy things up.

It should be possible from the admin interface to:

• delete a resource, and associated attempts
• delete a context, and associated resources
• delete data corresponding to a particular person, identified by name or username
• delete all attempts older than a given age, and optionally any resources or contexts which are empty as a result.