Oauth extra values & profile

Feature to manage oauth extra values.

You can save extra values from passport json response.
To do that, you can define what you want save by this way : 
* `jsonname` is the key of the value in `profile._json`
* `localname` is the name of the key you want in database

`config/passport.js`
```js
github: {
    name: 'GitHub',
    protocol: 'oauth2',
    strategy: require('passport-github').Strategy,
    options: {
      clientID: 'your-client-id',
      clientSecret: 'your-client-secret'
    },
    paths: {
       jsonname: 'localname'
    }
}
```

And set property in Profile model : 
`api/models/Profile.js`
```js
attributes: {

    github: { model: 'Oauth', required: false },

    // Associations
    // ...
    user: { model: 'User', required: true }
}
```


Thank you @kasperisager for your advice, this code works more in your vision. 
If you have other tips to improve this feature, I'm always open to the proposal