add support for disabled buttons and backButtonHidden on push

example/src/screens/SecondTabScreen.js

@@ -56,7 +56,8 @@ export default class SecondTabScreen extends Component {
       buttons = [
         {
           title: 'Edit',
-          id: 'edit'
+          id: 'edit',
+          disabled: true
         },
         {
           icon: require('../../img/navicon_add.png'),

src/platformSpecific.ios.js

@@ -185,6 +185,7 @@ function navigatorPush(navigator, params) {
     passProps: passProps,
     style: navigatorStyle,
     backButtonTitle: params.backButtonTitle,
+    backButtonHidden: params.backButtonHidden,
     leftButtons: navigatorButtons.leftButtons,
     rightButtons: navigatorButtons.rightButtons
   });