Remove `qucosa:` prefix in document links
Retrieve document by QucosaID
Use ResponseEntity as return value

Preparation for returning meaningful HTTP status codes.
Return HTTP Status Codes

- 200 when a response can be rendered
- 401 if there is no authorization
- 404 if there is no such document
- 500 if something goes wrong
Improve POM artifact identification
Generic role-parameter based authentication

HTTP requests normally need HTTP BasicAuth. To enable legacy Qucosa role based authentication, a `role` parameter can be passed in the request URL instead of BasicAuth headers.