irc/irssi: Update to 1.0.6, Fixes multiple security vulnerabilities

While here, update license and www.

Changes: https://raw.githubusercontent.com/irssi/irssi/1.0.6/NEWS

PR: 224954
Submitted by: David O'Rourke <dor.bsd@xm0.uk> (maintainer)
Reported by: tj@mrsk.me (email)
MFH: 2018Q1
Security: a3764767-f31e-11e7-95f2-005056925db4