New buttons

Styles for the new buttons. 

I've added a [hack](https://github.com/lonelyplanet/rizzo/commit/9f443e66ad287147f780298c036e33c4f6651259) to avoid problems in the buttons transition. So, by default, the `.btn` class will have `.btn--medium` and `.btn--linkblue`. This is only temporary, I will delete it after the changes in all the applications. It's only to make the transition to the new buttons easier. 

This is how they look:
![lonely planet travel guides and travel information](https://cloud.githubusercontent.com/assets/1152640/5200442/616745d0-7566-11e4-8534-5d034c67235b.png)