Ban automatically Excess Flood hosts on #wikipedia-fr

Summary:
If an unknown user from specified hosts quits in Excess flood,
with a 3-5 nick length, the bot will automatically put a ban.

New registry keys:

• protection.botnet.hosts: the hosts to ban, * allowed
• protection.botnet.banreason: the ban reason
• protection.botnet.banduration: the ban duration in minutes

New helper procedures in core:

• gethost: extracts the host part of a [nick!]user@host string
• isipv4, isipv6, isip: determines if a string is an ip

Fixes T515.

Test Plan:

• Deploy on Daeghrefn
• See how it behaves at the next attack

Subscribers: rama

Projects: #d?ghrefn, Wikimedia

Maniphest Tasks: T515

Differential Revision: http://devcentral.nasqueron.org/D31