refact(ionBar): interpolate title instead of binding

BREAKING CHANGE:

ionHeaderBar's title attribute is now interpolated.

Change this code: `<ion-header-bar title="myTitleVar"></ion-header-bar>`

To this code: `<ion-header-bar title="{{myTitleVar}}"></ion-header-bar>`

js/ext/angular/src/directive/ionicBar.js

@@ -76,7 +76,6 @@ angular.module('ionic.ui.header', ['ngAnimate', 'ngSanitize'])
       type: '@',
       alignTitle: '@'
     },
-
     link: function($scope, $element, $attr) {
       var hb = new ionic.views.HeaderBar({
         el: $element[0],