* Added OneSignal wrapper
* documentation
* Changes for callback of notification revieced
* fixes for @Cordova decorators without Promise return
* Merge
* Improvements to OneSignal
extended init function with notificationOpenedCallback as an optional parameter
* Platforms removed
OneSignal supports more than only these 3 platforms. It's available to nearly all Cordova platforms.
* Init method turned into observable
* Screen Orientation Plugin added. Closes#342
