Merge branch '2.4' into 2.5

CHANGELOG.md

 # Changelog
 
+## 2.4.3
+This release fixes a performance issue on session creation affecting large
+installations.
+
+Bug fixes:
+* WebSocket communication now works correctly for course sessions.
+  (only affects installations using the LMS connector)
+* The configuration parameter `security.facebook.allowed-roles` is now
+  respected.
+
+Additional changes:
+* Libraries have been upgraded to fix potential bugs
+
 ## 2.5
 Major features:
 * Administration API: New endpoints have been added which are accessible by

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

@@ -522,9 +522,9 @@ public class CouchDBDao implements IDatabaseDao, ApplicationEventPublisherAware
 	}
 
 	@Override
-	@Transactional(isolation = Isolation.READ_COMMITTED)
 	public boolean sessionKeyAvailable(final String keyword) {
 		final View view = new View("session/by_keyword");
+		view.setKey(keyword);
 		final ViewResults results = getDatabase().view(view);
 
 		return !results.containsKey(keyword);