Add TcpConnection tests and fix noticed bugs. Also some minor improvements were done.
Remove secure_name_label GtkLabel from ConnectionRow.
Introduce ErrorCallback in Listener.
Update Service due to changes in other classes.
Simplify Connections::lookup().
Add some assertions and DEBUG_MESSAGE macros to Neighbourhood.
All callbacks are mandatory in Listener and Connection based classes. passing empty callback will raise assertions.
Update TcpConnection tests.