Add a flag to the bulk delete script to restrict to non @cam.ac.uk email addresses

Add a flag to the bulk delete script to restrict to non @cam.ac.uk email addresses. This is so we can do purges that do not remove students using Timetabler, as they may not have ever logged in. They will definitely have @cam.ac.uk emails though. Accounts with @cam.ac.uk will be purged using lists generated by UIS's databases of people who have left the University and the functionality that takes a filename.