GDPR handling

[chriskapp]

We should think about adding some features to simplify GDPR handling.

• At the backend we could add a panel where an admin can delete all data for a specific user if the user requests this.
• At the developer app we may also add a panel where a user can export all records which are assigned to his account.
• At a plain Fusio installation we have only the fusio_log and fusio_token table which we need to cover
• If there a custom app tables, Fusio somehow needs to know which tables are affected