authenticate using appStoreRecipt
Checking iOS in-app purchase receipt with iTunes, and returning the body if that article has been purchased or the receipt contains a subscription with an expiry date greater than now.
Added newsstand.json and newsstand.xml for feeding iTunesconnect and in app purchases.
Sorting newsstand.json and newsstand.xml by reverse issue number.
authenticated access to article#body with a test (that doesn't work in guard)
Merge branch 'appStoreReceipt' of github.com:sighmon/NI into appStoreReceipt

Conflicts:
	app/controllers/articles_controller.rb
Fixed icon URL bug in newsstand.xml
Merge branch 'appStoreReceipt' of github.com:sighmon/NI into appStoreReceipt
Added inapp.xml for iTunesConnect and updated name for in app purchases of single issues to XXXsingle
Fixed receipt checking code for single issue purchases.
Start date for inapp.xml is now today minus one day.
Fixed the iTunes in app receipt checker to handle non-renewing subscriptions.
json auth test moved to controller spec
fall through devise and then itunes authentication for article#body
test ip whitelisting of child users
Merging appStoreReceipt to master.