Support for RefreshToken, RenewIdToken and token exp validation for Android and iOS

@mgonto mind reviewing? still need to update the implementation to get the dev id/name in Android.

@tvand7093: this is the updated PR.
I think this should be:

````js
emptyToken && (this.CurrentUser == null || string.IsNullOrEmpty(this.CurrentUser.RefreshToken))
````

You're not checking for `CurrentUser`