pcap: filename chooser

[jasonish]

          > Better for sure. Do you think there is anything else that should go in that filename?

I guess in my workflow I would call something inliniac-public-sid-12345-dns-blah.pcap, so maybe at least the app proto? But an option that would present a text box could also work, but not sure how that would work here.

Originally posted by @victorjulien in #319 (comment)