move requiring sign in to its own function

There's probably a proper Nancy-ish way to do this, but I don't know if
it'd play nice with my functional approach, and this works. So, I'm
running with it.
make /ooc the default when no slash command

When no slash command is given (i.e., text without a starting slash is
posted), treat is as an /occ slash command. I'm really not sure this is
the best thing to do, but I do no requiring the slash is too confusing.
I think more work will have to be done to make using slash command
intuitive.