Feature cookbooks

:fork_and_knife: Allows Supermarket admins to feature cookbooks and displays them on the cookbooks directory.

![screen shot 2014-07-22 at 4 47 43 pm](https://cloud.githubusercontent.com/assets/316507/3664961/70af2d16-11e1-11e4-947b-f26d4154305a.png)

![screen shot 2014-07-22 at 4 42 08 pm](https://cloud.githubusercontent.com/assets/316507/3664936/4da56c90-11e1-11e4-9513-9dec781d9617.png)