feat: projects on overview-student are built from DB

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

...ava/unipotsdam/gf/core/management/project/ProjectDAO.java

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

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

gemeinsamforschen/src/main/webapp/core/templates.js

gemeinsamforschen/src/main/webapp/enroll-project.jsp

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