Diagnostic messages should be copyable from the window

[vi]

E.g. "No traffic can be observed because the adapter you selected has no active addresses" should be easy to copy and paste to a bug report.

Alternatively, some of the messages displayed in GUI can be duplicated to stderr.

[GyulyVGC]

Unfortunately, the library I used doesn't support text selection in GUI.

I could consider adding messages on stdout, thanks!