Use client-only collection for items

Hi, i was checking out GridLayout on http://famous-components.meteor.com

I was assuming ‘Items' is a client-only collection and in order to try a few things, first i removed all items in collection with following:

```js
Items.find().forEach(function(item) { Items.remove(item._id)} );
```

I realized that it's a db collection when i opened another tab. Now there is only one item in Items collection at http://famous-components.meteor.com

I converted it into client only collection to avoid problems like this in the future.