* JsonHelper.cs: Helper methods for serializing/deserializing json
  files

* AppModelParam.cs: Encapsulates AppModels supplied as parameters

* Consts.cs: added new constants

* AppModel.cs: Added AppModelRoot encapsulating a list of AppModels

* AppReview.cs: Added AppReviewRoot encapsulating a list of AppReviews

* packages.config: Added the package Newtonsoft.Json