Support echoing output from other clients

in the zmq console

Can result in outputs like:

```
In [1]: 1
[remote]In [1]: 1
[remote]Out[1]: 1
[remote]In [2]: 3
[remote]Out[2]: 3
Out[3]: 1
```

Note that there will be inconsistencies in prompt numbers because some execution may take place after the in-prompt is drawn.

closes #1873
Looks like you got half way through writing this - it should presumably end like "... until you next run code here."