feat: Alter submission parts to use array as body

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

...f/modules/submission/controller/SubmissionController.java

...nipotsdam/gf/modules/submission/model/SubmissionPart.java

...f/modules/submission/model/SubmissionPartBodyElement.java

...f/modules/submission/model/SubmissionPartPostRequest.java

...potsdam/gf/modules/submission/view/SubmissionService.java

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

gemeinsamforschen/src/scripts/dbschema/fltrail.sql