Add user verification for admin commands

hi @whimboo !

here's a patch for issue #28. I've run some quick tests on it, seems ok.
this could perhaps still be tidied up some, but it is far better than the code it replaces in the first patch.
I've added some error-checking and tweaked the adminhelp array to support all this.
Hi @whimboo !
This code does already allow actions only for registered and identified nicks, via the checks at the top of the admin commands block.
The error handler at https://www.npmjs.com/package/irc#help-it-keeps-crashing- is already part of the bot's code.
I've reported an issue with node-irc: https://github.com/martynsmith/node-irc/issues/267
I'll add an issue here to update (or replace, maybe https://github.com/oftn/oftn-bot) the library.