Implement nickserv auth in hubot-irc

[patcon]

Reticketed from #12

See nandub/hubot-irc#103

[patcon]

Had a quick convo with @technicalpickles on IRC about GitHub's ues of yubikeys, sparked from seeing their yubikey-invalidation hubot script. Seems they use the nano, mostly for SSH auth, but in theory, we could have hubot PM the person running the privileged hubot command, and expect a valid yubikey OTP in reply.

Anyhow, just wanted to get the thought down somewhere public :)

Thanks @technicalpickles!

[seanlinsley]

That'd be awesome