Zmq app

There is an ugly if that checks if the response is a list or not. And if it is a list it iterates through it and sends all elements of that response list. 

So, except the scenario when the target sends multiple documents, other responses are contained upto a single message only. In those cases, I was just wondering whether it might be a better idea to just send the `response` message as `[response]`. That way, a single general if would look like:

```
    if response:
        for r in response:
             # Do whatever needs to be done with r.
```