Properly handle binding to loopback on mixed IPV4/IPV6 systems

The current issue with the cookbook is it specifies loopback in the main.cfg for the NICs to bind to, but it specifies the networks to just 127.0.0.1. In the current release postfix prefers the IPV6 stack, but we don't bind to the IPV6 loopback. End result is postfix doesn't work. If you don't specify the network entirely it will handle the config correctly internally. On systems with IPV4 only it will write out 127.0.0.1, and on dual stack environments you'll get both loopbacks. So now we can just specify the attribute for my networks as nil and let the daemon handle the logic. This same logic lets someone avoid writing out any attribute in the cookbook, which might be handy for other attributes

And while I'm in here I updated modes to strings and copyrights / e-mails for Chef Software vs. Opscode.