New option to delete an organization

[Fasse]

We should add an option in the preferences to delete the current organization. This should only available if there is more than 1 organization in the database. There must also be a separate call for username and password of a webmaster. If this is passed than all data of the organization should be deleted. Data to delete: announcements events downloads fotos guestbook lists weblinks roles memberships registrations preferences

Data not delete: users

[Bullnados]

I would say its just available after a Backup, preventifely