menuscreen, loginscreen, levelscreen are working as so far...
updated Screen-classes to "extends AbstractScreen"
updated
added userdata.json
Merge branch 'master' of https://github.com/Internship-AURIS/Project-AURIS

Conflicts:
	core/src/com/aau/auris/game/screens/LevelScreen.java
	core/src/com/aau/auris/game/screens/LoginScreen.java