[MovieApp] Add key to image components inside of MovieCell.

Summary:
Closes https://github.com/facebook/react-native/pull/2065
Github Author: Christopher <hello@blick-labs.com>

Examples/Movies/SearchScreen.js

@@ -262,6 +262,7 @@ var SearchScreen = React.createClass({
   ) {
     return (
       <MovieCell
+        key={movie.id}
         onSelect={() => this.selectMovie(movie)}
         onHighlight={() => highlightRowFunc(sectionID, rowID)}
         onUnhighlight={() => highlightRowFunc(null, null)}