Authentication

Hi
Thanks for sharing this project. I've started an authentication flow and the model changes so I can have different users and each one will have their probes. I've tried to keep it simple and understand the architecture but at this point I'd like some help reviewing it.
If you dont think this is the right approach please let me know. Also, if you think that auth is not the way to go I'd ask you if you mind that I keep this branch around (I can even rename it or put a message on the README).
There is a create_user.js script in the home dir to create the first user but I think that a /admin interface would be better.
Thanks