Added isOpen function for the listener

Author: jorisadri

src/infrastructure/Listener.ts

@@ -157,6 +157,17 @@ export class Listener {
         });
     }
 
+  /**
+     * returns a boolean that repressents the open state
+     * @returns a boolean
+     */
+    public isOpen(): boolean {
+        if(this.webSocket){
+            return this.webSocket.readyState === WebSocket.OPEN;
+        }
+        return false;
+    }
+    
     /**
      * Close web socket connection.
      * @returns void