Add ionicTabs#showBar() method to set/get whether the tabs bar is shown

[shaoner]

Ability to hide the tabs bar from a controller:

$scope.$on('$ionicView.afterEnter', function () {
  $ionicTabsDelegate.$getByHandle('my-tab-bar').showBar(false);
});

$scope.$on('$ionicView.beforeLeave', function () {
  $ionicTabsDelegate.$getByHandle('my-tab-bar').showBar(true);
});

[mlynch]

Thanks! Tested this and it works well.