Netviz cleanup and tweaks as follow:

Added axis lines to all plots via base class
commented-out code scrub
Report now displays the input filename as given by the BE API
Report header now includes generation time
added missing packet ingestion for port histograms
Changed from binary byte count prefixes to SI (was using SI in actuality anyway)
Added packetfall placeholder
no longer creates transcripts or attachments for zero-length files
Merge branch 'master' of github.com:simsong/tcpflow