Related to #114 : Favorite searches support

I added a simple support for favorite searches management (add, open, delete) to kibana-ruby-auth. It adds a dropdown menu to the search bar and uses Fancybox (http://fancybox.net) to display modal windows. 
![image](https://f.cloud.github.com/assets/2794902/81348/2e589b70-631c-11e2-8d2c-141cae2bedde.png)
![image](https://f.cloud.github.com/assets/2794902/81350/55984ac8-631c-11e2-84e0-5e636012c777.png)

The favorites (in fact the page hashcode) are stored in the defined storage backend of kibana-ruby-auth (currently only elasticsearch is supported).
I added an /api/favorites API for this purpose.

Maybe you shouldn't merge this yet. Indeed, I don't know if the page hashcodes should be saved as favorites. What about transient URLs ? Also, little work is needed for kibana-ruby-auth to be usable in production. It would be great to merge both branches ASAP. User management, role based access control and favorites searches are must-have features!