Rename the script to update-firewall, and add update-ipset

Moves the ipset file-based configuration to a directory hierarchy
below /etc/firewall/blocked, with "type" (ip/net) and "proto"
(ipv4/ipv6) nested subdirectories and a run-parts-style multi-file
setup.

Allows users to update ipsets without having to necessarily reload
all the other firewall rules.