Start of more OSX facts for setup

Added a Darwin family, commit acc1c004 had added some network facts
but weren't being shown as the Darwin family wasn't in use. This commit
reveals these facts.

A Darwin(Hardware) class has also been created ready to be populated with
hardware facts.

It turned out to be fairly minimal in what I wanted as the networking information/code was already there. It's now enabled and being shown when the setup module is run.