Deleting of users

[bedhub]

As an admin of a Tutanota account i want to be able to delete users from my account so that the data of that user gets deleted and i don't see them in the list of users anymore.

Acceptance criteria

• [ ] Delete action removes the user from the user list.
• [ ] Mails, calendar and contact data is deleted and the used data is not counted anymore.
• [ ] Custom domain email aliase can be used again.
• [ ] Tutanota domain aliases can only be used by the same customer and not by other customers.