iOS decoded receipt (local validation)

[mircoc]

I added a method to decode the receipt locally on iOs.

It return something like this:

inAppPurchase.getReceiptBundle().then(function(res){console.log("receipt:",res)})
receipt:
appVersion: "0.1.0"
bundleIdentifier: "com.mycompany.myproduct"
inAppPurchases: 
  cancellationDate: null
  originalPurchaseDate: "2016-07-05T10:15:22Z"
  originalTransactionIdentifier: "1000000221696692"
  productId: "com.mycompany.myproduct.weekly.v1"
  purchaseDate: "2016-07-05T10:15:21Z"
  quantity: 1
  subscriptionExpirationDate: "2016-07-05T10:18:21Z"
  transactionIdentifier: "1000000221696692"
  webOrderLineItemID: -1497665198
originalAppVersion: "1.0"

I'll update the PR with test asap.

Let me know what you think,
thanks!

[coveralls]

Coverage decreased (-8.2%) to 76.471% when pulling a54ca4c on D-Mobilelab:master into 27262e5 on AlexDisler:master.

[coveralls]

Coverage decreased (-8.2%) to 76.471% when pulling 03371f2 on D-Mobilelab:master into 27262e5 on AlexDisler:master.

[coveralls]

Coverage increased (+1.3%) to 85.938% when pulling 4b3c648 on D-Mobilelab:master into 27262e5 on AlexDisler:master.