refactor: The attribute 'targetId' is now a String

...n/src/main/java/unipotsdam/gf/interfaces/IAnnotation.java

...f/modules/annotation/controller/AnnotationController.java

...va/unipotsdam/gf/modules/annotation/model/Annotation.java

...am/gf/modules/annotation/model/AnnotationPostRequest.java

...potsdam/gf/modules/annotation/view/AnnotationService.java

...m/gf/modules/annotation/websocket/AnnotationWSTarget.java

...les/annotation/websocket/AnnotationWebSocketEndpoint.java

...samforschen/src/main/webapp/assets/js/annotationScript.js

...forschen/src/main/webapp/assets/js/annotationWebsocket.js

gemeinsamforschen/src/scripts/dbschema/fltrail.sql

...rc/test/java/unipotsdam/gf/interfaces/AnnotationTest.java