feat(templateCache): automatically cache template files to prevent flicker on page navigation and improve performance

State templates are cached automatically, but you can optionally cache other templates.
```js
$ionicTemplateCahce('myNgIncludeTemplate.html');
```

Optionally disable all preemptive caching with the `$ionicConfigProvider` or individual states by setting `prefetchTemplate`
in the $state definition
```js
$ionicTemplateCahce('myNgIncludeTemplate.html');
```js
  angular.module('myApp', ['ionic'])
  .config(function($stateProvider, $ionicConfigProvider) {

    // disable preemptive template caching globally
    $ionicConfigProvider.prefetchTemplates(false);

    // disable individual states
    $stateProvider
      .state('tabs', {
        url: "/tab",
        abstract: true,
        prefetchTemplate: false,
        templateUrl: "tabs-templates/tabs.html"
      })
      .state('tabs.home', {
        url: "/home",
        views: {
          'home-tab': {
            prefetchTemplate: false,
            templateUrl: "tabs-templates/home.html",
            controller: 'HomeTabCtrl'
          }
        }
      });
  });
```