refactoring: switching to dependency injection and fixing tests

...c/main/java/unipotsdam/gf/modules/project/ProjectDAO.java

.../main/java/unipotsdam/gf/modules/project/ProjectView.java

...rschen/src/main/webapp/groupfinding/enter-preferences.jsp

...hen/src/main/webapp/groupfinding/js/create-preferences.js

gemeinsamforschen/src/main/webapp/project/js/join-project.js

...amforschen/src/main/webapp/project/js/overview-student.js

...nsamforschen/src/main/webapp/project/overview-student.jsp

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

...insamforschen/src/main/webapp/project/project-student.jsp

gemeinsamforschen/src/main/webapp/taglibs/js/utility.js