WIP: Delete User

[crosspolar]

When deleting a user:

• Send confirmation with all user information (shift history, payment history, etc.) to certain mail for archiving
• Anonymize personal data but keep user to maintain statistics
• Mark user as deleted
• Corresponding DraftUser has to be deleted to, if exists (has only Cascade Delete)

Preparation:

• To have a trunk TapirUser without personal information which only gets soft-deleted when deleting a user. For that, we need to A) move "Personal Information" (address, name, etc.) to new model PersonalInformation which gets linked to the user and B) move Co-Purchaser to new model.
• Log-Entrys should not save historic data. If we need historic data, it could be stored in an extra model with daily snapshots of e.g. number of Co-Purchasers.

Deleting

• Relations to delete: PersonalInformation, CoPurchaser, LogEntry

Other ways

• Anonymization: This would mean, we just replace address, mail, etc. with fuzzy information or None.