Native Http handlers = better performance

See this: https://github.com/luberda-molinet/FFImageLoading/issues/441#issuecomment-271714973

#iOS

ImageService.Instance.Initialize(new Configuration
{
	HttpClient = new HttpClient(new NSUrlSessionHandler() 
	{
		AutomaticDecompression = DecompressionMethods.GZip | DecompressionMethods.Deflate, 
	})
});

Android

ImageService.Instance.Initialize(new Configuration
{
	HttpClient = new HttpClient(new AndroidClientHandler() 
	{
		AutomaticDecompression = DecompressionMethods.GZip | DecompressionMethods.Deflate, 
	})
});