Allowing turning on / off DOM storage on android webviews

Summary:
Was developing on a WebView and couldnt get it to run. Turns out its JS code mostly depends on `localStorage` and I realized it wasnt turned on in RN. This PR adds a prop, similar to `javascriptEnabledAndroid` to be able to turn DOM storage on / off.

TBH I dont really know how it works on IOS, so I created an android specific thingy. I assume DOM storage is enabled by default on IOS.
Closes https://github.com/facebook/react-native/pull/5065

Reviewed By: svcscm

Differential Revision: D2797735

Pulled By: androidtrunkagent

fb-gh-sync-id: cd60cfa4d24d80fb82e4f54f387a4517a99e75ab

Examples/UIExplorer/WebViewExample.js

@@ -95,6 +95,7 @@ var WebViewExample = React.createClass({
           style={styles.webView}
           url={this.state.url}
           javaScriptEnabledAndroid={true}
+          domStorageEnabledAndroid={true}
           onNavigationStateChange={this.onNavigationStateChange}
           onShouldStartLoadWithRequest={this.onShouldStartLoadWithRequest}
           startInLoadingState={true}