[5.3] Allow chaining factory calls to define() and state()

[shadoWalker89]

This will allow to group each Model definitions

/**
 * Teacher
 */
$factory
    ->define(App\Teacher::class, function (Faker\Generator $faker)
    {
        return [
            //
        ];
    })
    ->state(App\Teacher::class, 'teacher_foo_state', function (Faker\Generator $faker) {
        return [
            //
        ];
    })
    ->state(App\Teacher::class, 'teacher_bar_state', function (Faker\Generator $faker) {
        return [
            //
        ];
    });

/**
 * Student
 */
$factory
    ->define(App\Student::class, function (Faker\Generator $faker)
    {
        return [
            //
        ];
    })
    ->state(App\Student::class, 'student_foo_state', function (Faker\Generator $faker) {
        return [
            //
        ];
    })
    ->state(App\Student::class, 'student_bar_state', function (Faker\Generator $faker) {
        return [
            //
        ];
    });