Add slider thumbnail reel feature

![screen shot 2014-10-17 at 10 49 36 am](https://cloud.githubusercontent.com/assets/2614324/4681671/38b82c50-5615-11e4-9035-0453602d5cdc.png)


We have a handy mixin for this now https://github.com/lonelyplanet/rizzo/blob/master/app/assets/stylesheets/sass/mixins/_css3.sass#L11