Add display by host name option to Traffic Graph

I think this version is now better than the one I did at https://github.com/bsdperimeter/pfsense/pull/443
Now it is easy for users to disable forwarding of private IP PTR lookups to upstream routers - commit https://github.com/bsdperimeter/pfsense/commit/b710a07883fbc0a462e5aad6bf6f6d85f1126615
They can easily ensure that gethostbyaddr() lookups of unknown private IPs on the local LAN do not get forwarded off to the internet DNServers. That avoids any issue with possible delays in gethostbyaddr() responses.
This change primarily uses gethostbyaddr() to find the name that corresponds to each of the top bandwidth offenders. Only the first bit of the name is displayed - as in many cases displaying the FQDN causes clutter/wrapping in the display column. In most cases the names are local internal names anyway, so the domain portion is repetitive.