Friendlier `--dev-mode` error message, new `help` command

![screen shot 2014-10-17 at 7 46 39 am](https://cloud.githubusercontent.com/assets/163977/4678263/574fab74-55f3-11e4-9630-4f6169e9d584.png)

If you put the server in dev mode it will be a private address. You also made it disable stun check so it goes here and the assert says no way to the private address. That's how.