Add default values for ion-view hide-back-button and hide-nav-bar attributes

If your view is missing the hide-back-button or hide-nav-bar attributes, we get exceptions from Angular when trying to watch these non-existent properties.

i.e.
```
TypeError: Cannot read property 'exp' of undefined
    at ng.config.$provide.decorator.watchFnToHumanReadableString (<anonymous>:703:19)
    at Scope.ng.config.$provide.decorator.$delegate.__proto__.$watch (<anonymous>:735:28)
    at link (http://localhost:3000/bower_components/ionic/release/js/ionic.bundle.js:37265:16)
    at nodeLinkFn (http://localhost:3000/bower_components/ionic/release/js/ionic.bundle.js:13700:13)
    at compositeLinkFn (http://localhost:3000/bower_components/ionic/release/js/ionic.bundle.js:13110:15)
    at publicLinkFn (http://localhost:3000/bower_components/ionic/release/js/ionic.bundle.js:13015:30)
    at updateView (http://localhost:3000/bower_components/ionic/release/js/ionic.bundle.js:37466:11)
    at angular.module.directive.directive.directive.compile.eventHook (http://localhost:3000/bower_components/ionic/release/js/ionic.bundle.js:37410:17)
    at Scope.$get.Scope.$broadcast (http://localhost:3000/bower_components/ionic/release/js/ionic.bundle.js:19731:28)
    at t.transitionTo.t.transition.N.then.t.transition.t.transition (http://localhost:3000/bower_components/angular-ui-router/release/angular-ui-router.min.js:7:10007) <ion-view class="pane">
```

Fixed by adding default values of false for both attributes (which should stand by undefined == false and that the default behaviour should be to show the nav bar and the back button if possible).