feat(ionic): prefix all directives with ion-

BREAKING CHANGE: All directives are now prefixed with `ion-`.

For any directive you use, add the ionic prefix.

For example, change this HTML:

```html
<tabs>
  <tab title="home" href="/tab/home">
    <content>Hello!</content>
  </tab>
</tabs>
```

To this HTML:

```
<ion-tabs>
  <ion-tab title="home" href="/tab/home">
    <ion-content>Hello!</ion-content>
  </ion-tab>
</ion-tabs>
```

js/ext/angular/src/service/ionicLoading.js

@@ -31,7 +31,7 @@ angular.module('ionic.service.loading', ['ionic.ui.loading'])
       }
 
       // Compile the template
-      var element = $compile('<loading>' + opts.content + '</loading>')(scope);
+      var element = $compile('<ion-loading>' + opts.content + '</ion-loading>')(scope);
 
       $document[0].body.appendChild(element[0]);