Android. Add native callback when Push message received

[KirillAshikhmin]

For avoid 01-29 14:20:35.280: E/AndroidRuntime(31479): java.lang.Error: md52ce486a14f4bcd95899665e9d932190b.JavaProxyThrowable: System.InvalidOperationException: You MUST call Xamarin.Forms.Init(); prior to using it. 01-29 14:20:35.280: E/AndroidRuntime(31479): at Xamarin.Forms.Device.get_PlatformServices () [0x00007] in <filename unknown>:0 01-29 14:20:35.280: E/AndroidRuntime(31479): at Xamarin.Forms.Device.GetAssemblies () [0x00000] in <filename unknown>:0 01-29 14:20:35.280: E/AndroidRuntime(31479): at Xamarin.Forms.DependencyService.Initialize () [0x00000] in <filename unknown>:0 01-29 14:20:35.280: E/AndroidRuntime(31479): at Xamarin.Forms.DependencyService.Get[T] (DependencyFetchTarget fetchTarget) [0x00007] in <filename unknown>:0

And dor call native fuction