add callback after created controller.

Sometimes view controller has data.
The controller was set as a root view controller to the window before called "before" block.
But a data is not set at this point.
The view controller access to nil, and crash sometime even if I set data in "before" block.

After created controller it will call the specified callback method if you set :after_created option

# Example
```ruby
# my_view_controller_spec.rb
describe MyViewController do

  tests MyViewController, after_created: :after_created_controller

  def after_created_controller controller
    # you can set data to the controller here
    controller.my_data = "foo"
  end

  .
  .
end