Update Image docs and examples to the new asset system

Summary:
After the release of 0.14, static images should be placed in the source code tree and then required as explained in the [Images guide] (https://facebook.github.io/react-native/docs/images.html). This pull request updates the image documentation and examples to the new asset system. UIExplorer tested on iOS and Android.
Closes https://github.com/facebook/react-native/pull/4987

Reviewed By: svcscm

Differential Revision: D2796276

Pulled By: bestander

fb-gh-sync-id: 732ffa2f136391bb8a3e40a54b5b1ff5022c97f2

Libraries/Image/Image.android.js

@@ -38,7 +38,7 @@ var resolveAssetSource = require('resolveAssetSource');
  *       <View>
  *         <Image
  *           style={styles.icon}
- *           source={require('image!myIcon')}
+ *           source={require('./myIcon.png')}
  *         />
  *         <Image
  *           style={styles.logo}
@@ -66,8 +66,8 @@ var Image = React.createClass({
     style: StyleSheetPropType(ImageStylePropTypes), 
    /**
      * `uri` is a string representing the resource identifier for the image, which
-     * could be an http address, a local file path, or the name of a static image
-     * resource (which should be wrapped in the `require('image!name')` function).
+     * could be an http address, a local file path, or a static image
+     * resource (which should be wrapped in the `require('./path/to/image.png')` function).
      */
     source: PropTypes.oneOfType([
       PropTypes.shape({