Add non-required authentication (including user account management) to the application

[bhermann]

For more advanced features, we require registered, authenticated users.
To achieve this, please add authentication and user management to this application.
This was previously done in delphi-hub/delphi-management#11 and delphi-hub/delphi-management#12.

We really have to think hard here if it is wise to have a single user pool or a separate user management.