Store the user items selection on cookie

This PR is related to issue #20 and it's working in progress because I need create tests.

![fm-store-user-selection-on-cookie](https://cloud.githubusercontent.com/assets/1503773/5240038/d22f5c08-78e0-11e4-8211-df980d113047.gif)
I would create this similar structure with hash but I notice that cookies don't work well with Hash, it's become necessary create code to convert again to Hash when I tried access the value.

Like this:
```ruby
cookies[:background] = { value { :name => "value", :slug: "slug" } }
```
For access this I needed use gsub methods to convert again to Hash and I thought it's not necessary at this moment.