feat: reworked menu for student, docent and missing tag.

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

...rc/main/java/unipotsdam/gf/core/management/user/Menu.java

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

gemeinsamforschen/src/main/webapp/index.jsp

...amforschen/src/main/webapp/pages/assessmentCalculator.jsp

gemeinsamforschen/src/main/webapp/pages/finalAssessments.jsp

gemeinsamforschen/src/main/webapp/pages/overview-docent.html

gemeinsamforschen/src/main/webapp/pages/overview-docent.jsp

...insamforschen/src/main/webapp/pages/overview-student.html

gemeinsamforschen/src/main/webapp/pages/overview-student.jsp

gemeinsamforschen/src/main/webapp/pages/takeQuiz.jsp