Implement connection loss detection

[mremond]

We need to use whitespace ping to maintain the connection and basically "ask" the network layer if the connection is still valid.
It should also solve #8.

I will not support XMPP ping for now as it is much more consuming for both the client and the server (CPU and bandwidth) without providing any significant benefit for checking the client to server connection. XMPP ping should be limited to client to client and components interactions.