Vertical Stacks Reset (Option Added)

Added an option in the `Reveal.initialize({...})` configuration to automatically reset the vertical stack positions upon navigation:

```javascript
    config = {
           // ...

           // Automatically reset slideshow when home slide is viewed
           // Vertical slide stacks will go back to first slide
           // See Issue: #285
           autoHome: true,

           // ...
       },
```

Not totally sure if you wanted to have yet another option added to the configuration, but since this was a part of the reveal.js functionality and quite convenient, I just added it as an option. It has a 60ms (more) performance difference.

Reference Issue: #285