[Websocket] Messages duplication after modification

[nioc]

Hello,

After modifying the WS node (the Unifi url, for example) and redeploying, messages are sent twice, as we use the wslogin function with a timeout.

    node.tout = setTimeout(function () {
        node.status(STATUS_CONNECTING);
        wslogin();
    }, 5000);

The user must then restart Node-RED to clean up the previous event listeners.

Another problem I've encountered is that error handling sends the msg variable with the error in the according attribute, but if there was a previous onMessage event, the error also transmits it on.

I propose a fix in the Websocket refactoring of request #149 (which concerned WS functional improvements).