Add IgnoreNick config directive to ignore certain IRC nicks (ascii art bots, url echos, etc)

[yunginnanet]

I went ahead and hardcoded our artbot as an ignore into my copy. It should be fairly simple to make this a config directive as it is in Matterbridge. I'll fork at some point if I have time

[llmII]

This should be resolved (in a far better manner) in #82. Allows for ignoring IRC hostmasks.