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/test/java/de/thm/arsnova/config/TestAppConfig.java

@@ -45,6 +45,7 @@ import org.springframework.web.servlet.config.annotation.EnableWebMvc;
 		"de.thm.arsnova.aop",
 		"de.thm.arsnova.cache",
 		"de.thm.arsnova.controller",
+		"de.thm.arsnova.controller.handler",
 		"de.thm.arsnova.dao",
 		"de.thm.arsnova.events",
 		"de.thm.arsnova.security",