Merge branch 'master' into upstream

Conflicts:
	src/main/java/de/thm/arsnova/controller/SessionController.java
	src/main/java/de/thm/arsnova/dao/CouchDBDao.java
	src/main/java/de/thm/arsnova/dao/IDatabaseDao.java
	src/main/java/de/thm/arsnova/services/ISessionService.java
	src/main/java/de/thm/arsnova/services/SessionService.java
	src/test/java/de/thm/arsnova/dao/StubDatabaseDao.java