Sending and receiving heartbeat messages
Many Websocket applications implements heartbeat messages, called PING/PONG, to keep websocket connection alive. 

It will be great if DVWS has an option to add heartbeat messages. That will help testing manual established websocket connections from proxies like ZAP. In order to achieve that, we could use some parameters at ws-socket.php. An example: 

```
ws-socket.php --heartbeat--intervel <ms> --heartbeat-time <ms> 
```
I have being trying to implement that but i am not so familiar with javascript/php. 

Thank you :)