[Android] Fix for NullReferenceException when using the wrong activit… (#286)
[Android] Fix for NullReferenceException when using the wrong activit… (#286)

* [Android] Fix for NullReferenceException when using the wrong activity type.

On using FormsApplicationActivity or FormsAppCompatActivity as base Activity in a SplashScreen.
A NullReferenceException will be thrown in the KeyboardManager.
Added InvalidOperationException with "Forms.Init()" message instead, if the Forms.Context is null.

* Fixed indentation

Hitcents/Xamarin.Forms,Hitcents/Xamarin.Forms,Hitcents/Xamarin.Forms