Fix table setup and migrations

src/main/java/nl/tudelft/submit/model/Feedback.java

...n/java/nl/tudelft/submit/service/StudentGroupService.java

...ain/java/nl/tudelft/submit/service/SubmissionService.java

src/main/resources/migrations.yaml

src/main/resources/table-setup.yaml

src/main/resources/templates/submission/feedback.html

src/test/resources/application.yaml