Add IRC notifier

The base of this code is largely taken from [this old repo](https://github.com/sr/integrity-irc) which I tweaked a little to bring it up to date and added a (rather vague) test.

The IRC notifier has a tendency to time out if your IP address is firewalled and doesn't answer ident queries (assuming the network you are connecting to attempts to ident you). Once I opened up my ident port (but with nothing answering it) it worked just fine.

Hope this is all OK. We're using Integrity and are liking it so far! :smile: