Native implementation of <Image> intrinsic content size on iOS

Summary:
Now intrinsic content size of <Image> is implemented natively on iOS and now it is actually
`intrinsicContentSize`, not just overrided `height` and `width` styles (which was incorrect and hacky).
This change also removes support of nested content inside <Image>.
This is a first commit in the row where we improve <Image> implementation.

Reviewed By: mmmulani

Differential Revision: D5189017

fbshipit-source-id: eab3defa3d86a5d4219b4f4925ab7460b58d760f

RNTester/js/ImageExample.js

@@ -634,6 +634,18 @@ exports.examples = [
       return <ImageSizeExample source={fullImage} />;
     },
   },
+  {
+    title: 'Intrinsic Content Size',
+    description: 'Images have intrinsic content size which respects ' +
+      'to the first `source` image size.',
+    render: function() {
+      return (
+        <View>
+          <Image source={require('./uie_thumb_big.png')} style={{alignSelf: 'center'}} />
+        </View>
+      );
+    },
+  },
   {
     title: 'MultipleSourcesExample',
     description: