Adds Faker library to composer.json require/dev

- Adds `"fzaninotto/faker": "1.5.x-dev"` to require/dev
BaseApiController - First major shot at it. Provides sufficient methods.

Adds `abstract class BaseApiController`
- Extends Laravel's `\Controller`
- Various `respondDescription` methods
- Various getters/setters for format/data/etc...
- Utilizing `Illuminate\Http\Response` `const` properties for HTTP status codes

- Adds `behat.yml`
Todo\Models - Adds `protected $fillable` to models (not filled in)

- Minimal fillable set for User
Adds UsersController and index method to git via GET 'users' - WIP

WIP
- Temporarily adds in-line user generation class