Super admin routes for user and orga management

[normanrz]

Detailed Description

It would be very convenient to have the following routes available to super admins:

• Add an existing user to another organization (with user email/id, organization name)
• Create a new user that is automatically added to an organization (with names, email, password, organization name)
• Create a new organization (with organization name, owner user email/id)

Context

• Specific to long-running jobs (set jobsEnabled=true in application.conf)
• Specific to webknossos.org (set isDemoInstance=true in application.conf)