[NavigatorIOS] Allow translucent on NavigatorIOS

Summary:
Hi,

I've updated the NavigatorIOS component to allow setting the translucent property.

usage is:
```
            <NavigatorIOS
                translucent={false}
            />
```

This is my first contrib to react-native, so apologies if I've missed something.

Cheers,
Owen
Closes https://github.com/facebook/react-native/pull/1273
Github Author: Owen Kelly <owen@novede.com>

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

Examples/UIExplorer/NavigatorIOSColorsExample.js

@@ -66,6 +66,7 @@ var NavigatorIOSColors = React.createClass({
         tintColor="#FFFFFF"
         barTintColor="#183E63"
         titleTextColor="#FFFFFF"
+        translucent="true"
       />
     );
   },