TCP Link: Add backgorund behaviour to TCP Link

Once the TCPLink is started as a server, keep listening in the background for new TCP connections (as server).
Visually it is not optimal as the user doesn't really have a feedback that the link is awaiting connection (there is currently no such notion).
TCP Link: avoid NULL exception when the Link fires a disconnected event when the link is deleted.
TCP Link: automatically connects a TCPLink acting as server (like UDP Link)