Replace edit button on Pages with curation mode toggle widget.

Fixes #232 

`PagesController#show`
![screen shot 2014-02-18 at 12 17 13 pm](https://f.cloud.github.com/assets/96776/2199851/b7114bf8-98d9-11e3-8db5-2d11e28f5e4a.png)

`PagesController#edit`
![screen shot 2014-02-18 at 12 12 57 pm](https://f.cloud.github.com/assets/96776/2199855/bb8971c4-98d9-11e3-9cf9-e32b865d9944.png)