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)
It seems a good idea but when you use different identifiers in the same hash and store it on cookie you have some problems.
```ruby
cookies[:character_sheet] = { race_slug => race[:slug] }.to_json
```
It's work very well, when do you put another value inside the hash you get a problem.
```ruby
cookies[:character_sheet] = { race_variant_slug => race_variant[:slug] }.to_json
```
This replace the previous value, and if you use ```+=``` you got: ```{ race_slug => "value" } { race_variant_slug => "value" }```

I used separated cookies in this case.