replaced some IP magic numbers with constants

added IP4_ADDR_LEN and IP6_ADDR_len to iptree.h
minor plot_view refactor/cleanup

- moved constant initializers away from definitions
- cleaned up pretty_byte_total
  - moved to plot_view from one_page_report since it is useful in histogram
    views which should not logically depend on on_page_report
  - includes 'B' after size prefix since the output always represents bytes
  - has an optional precision parameter

pretty_byte_total now takes a precision argument
port and address histograms have y scales

histograms now have two ticks in their y scales for the min and max to aid in
quick visual estimation