also change creator when updating a session

src/main/java/de/thm/arsnova/dao/CouchDBDao.java

@@ -1559,6 +1559,7 @@ public class CouchDBDao implements IDatabaseDao, ApplicationEventPublisherAware
 		try {
 			final Document s = database.getDocument(session.get_id());
 			s.put("name", session.getName());
+			s.put("creator", session.getCreator());
 			s.put("shortName", session.getShortName());
 			s.put("active", session.isActive());
 			s.put("ppAuthorName", session.getPpAuthorName());

src/main/java/de/thm/arsnova/services/SessionService.java

@@ -320,6 +320,7 @@ public class SessionService implements ISessionService, ApplicationEventPublishe
 		existingSession.setPpLicense(session.getPpLicense());
 		existingSession.setPpSubject(session.getPpSubject());
 		existingSession.setFeedbackLock(session.getFeedbackLock());
+		existingSession.setCreator(session.getCreator());
 
 		handleLogo(session);
 		existingSession.setPpLogo(session.getPpLogo());