add WebSockets with STOMP on top

Adds a STOMP broker to the backend. Implements a standalone feedback with messages and topic channels.

This solves #25.

src/main/java/de/thm/arsnova/config/AppConfig.java

@@ -82,6 +82,7 @@ import java.util.List;
 @ComponentScan({
 		"de.thm.arsnova.cache",
 		"de.thm.arsnova.controller",
+		"de.thm.arsnova.controller.handler",
 		"de.thm.arsnova.event",
 		"de.thm.arsnova.security",
 		"de.thm.arsnova.service",