Restructuring the netfilter.org project homepage

Some years ago, the netfilter project only had the kernel side netfilter/iptables code, and the userspace iptables program. Then we added patch-o-matic(-ng), and more recently there were a number of more sub-projects growing, like ipset, all the nfnetlink-related code, ctnetlink, etc.

Unfortunately the homepage design didn't really cope with the fact that there is now a more hierarchical structure with many sub-projects.

It was always my hope that some "new webmaster" would take care of it. Unfortunately we still don't have a webmaster, so I spent some time on it today. You can see the results at www.netfilter.org.