stop tcp listening before app close

src/main/java/fr/insa/clavardator/users/UserList.java

@@ -184,6 +184,7 @@ public class UserList {
 	 */
 	public void destroy() {
 		netDiscoverer.stopDiscovery();
+		connectionListener.stopAccepting();
 //		db.close();
 		for (PeerUser user : activeUsers.values()) {
 			user.disconnect();