NavigatorIOS navigationBarHidden property support

Summary:
Usage example:
```javascript
var AwesomeProject = React.createClass({
  render: function() {
    return (
      <NavigatorIOS
        style={styles.navigator}
        navigationBarHidden={true}
        initialRoute={{
          component: Example,
          title: 'Test'
        }}
      />
    );
  }
});
```
Closes https://github.com/facebook/react-native/pull/374
Github Author: Kureev Alexey <kureev-mail@ya.ru>

Test Plan: Imported from GitHub, without a `Test Plan:` line.

React/Views/RCTWrapperViewController.m

@@ -65,7 +65,10 @@
   if ([self.parentViewController isKindOfClass:[UINavigationController class]])
   {
 
-    [self.navigationController setNavigationBarHidden:!_navItem animated:animated];
+    [self.navigationController
+      setNavigationBarHidden:_navItem.navigationBarHidden
+      animated:animated];
+
     if (!_navItem) {
       return;
     }