Add flag to keep clipper running

[SuperSandro2000]

When using on short lived commands like curl, there is barely enough time to connect the devtools. You could write the the data to a pcap file and then serve it or alternatively a flag could be added that clipper remains open after the command is done executing and continues to serve the devtools server until it is aborted with Ctrl+C.

[lf-]

This is a fair point. For now I would suggest running Clipper on a shell, but I can definitely see it being annoying even for GUI applications that it will auto-exit.