Added 'auto-play' as API's attribute to slideBox.js

Now you can use 'auto-play' and 'does-continue' as parameters separated.

```html
<ion-slide-box does-continue="true" auto-play="false">
    <ion-slide>Slide 1</ion-slide>
    <ion-slide>Slide 2</ion-slide>
    <ion-slide>Slide 3</ion-slide>
</ion-slide-box>
```