fix: login works with sessions again

...in/java/unipotsdam/gf/core/management/ManagementImpl.java

...nipotsdam/gf/core/management/pageAppearance/HeadLine.java

...va/unipotsdam/gf/core/management/pageAppearance/Menu.java

...va/unipotsdam/gf/core/management/project/ProjectView.java

...ava/unipotsdam/gf/core/management/user/HiddenUserTag.java

.../unipotsdam/gf/core/management/user/SessionValidator.java

...main/java/unipotsdam/gf/core/management/user/UserDAO.java

.../java/unipotsdam/gf/core/management/user/UserService.java

...tsdam/gf/modules/assessment/controller/view/QuizView.java

.../java/unipotsdam/gf/modules/communication/ChatWindow.java

...ules/communication/service/CommunicationDummyService.java

...otsdam/gf/modules/journal/service/JournalServiceImpl.java

...am/gf/modules/journal/service/ProjectDescriptionImpl.java

gemeinsamforschen/src/main/webapp/core/overview-student.js

.../java/unipotsdam/gf/core/management/user/UserDAOTest.java

gemeinsamforschen/src/test/resources/database/fltrail.sql