I realize that iOS 7 is not out yet and should not be discussed but I could not find the answer to this question anywhere and iOS 7 comes out in a few days.
I submitted
You can also use one asset catalog to organise your icon images, it's quite easy.If there is one image asset catalog, you use that one, otherwise you can new one. then select Use Asset Catalog in the App Icons part of General tab, you need to prepare the following image size and just drag the images to the corresponding location.
The icon sizes for iPhone and iPad for iOS 5~7 screenshot is as below:
or download it here