Is it possible to make Role::class extensible?

It would be useful to make Role class extensible. By adding it to config file in the same way as it was done for User model.

```
'userModel' => env('USER_MODEL', 'App\User'),
'roleModel' => env('ROLE_MODEL', 'Silvanite\Brandenburg\Role'),
```

At the moment it's impossible to extend your class functionality.