Create a more robust base configuration

[guumaster]

After discussing about configuration in #88, I think we should also make the service works with a more solid default configuration.

The idea is to have a really basic config and check features on service start and enable only the features that are correctly setup. Something like this:

{
   "features": {
      "pinValidation": true,
      "facebookLogin": true,
      "emailValidation": true,
      "magicLink": true
      /* features not explicitly set defaults to false */
   }
}

This way is really easy to start using the service and you know right away what to expect of it.

Also, what are your thoughts on allowing either config.json or a more readable config.yml file?