feat: Added Rest for project description, fix: Typo in Visibility enum

...ain/java/unipotsdam/gf/modules/journal/model/Journal.java

...ipotsdam/gf/modules/journal/model/ProjectDescription.java

.../java/unipotsdam/gf/modules/journal/model/Visibility.java

...tsdam/gf/modules/journal/service/DummyJournalService.java

...m/gf/modules/journal/service/DummyProjectDescription.java

...gf/modules/journal/service/ProjectDescriptionService.java

...tsdam/gf/modules/journal/view/ProjectDescriptionView.java