Open proxy checker

Summary:
Check the IP address of incoming user, with a blocklist by DNS.

Source: https://github.com/jamesoff/eggdrop-scripts/blob/master/ProxyCheck/proxycheck.tcl

Adapted for Freenode, to detect IPs in cloaks.

Fixes T913.

Test Plan:
Live test on Dæghrefn on #vikidia.

Works, and can extract IP address form gateway/ cloaks:

17:30 -!- ... [29e1d20a@gateway/web/cgi-irc/kiwiirc.com/ip.41.225.210.10] has joined #vikidia
17:30 -!- mode/#vikidia [+b *!*@gateway/web/cgi-irc/kiwiirc.com/ip.41.225.210.10] by Daeghrefn
17:30 -!- ... was kicked from #vikidia by Daeghrefn [Banni: proxycheck: xbl.spamhaus.org]

Reviewers: dereckson

Maniphest Tasks: T913

Differential Revision: https://devcentral.nasqueron.org/D475