Add delete folder button to web UI

This will add a `Delete folder` button to all folders, it will be disabled for the root folder. The delete request passes `?recurse` and will delete all underlying keys and folders. It might be a good idea to add a confirm dialog for this action in the future.

![screen shot 2014-05-05 at 02 13 12](https://cloud.githubusercontent.com/assets/190349/2874486/1ea57bf4-d3ea-11e3-8092-cb3269ed1290.png)

Resolves issue hashicorp/consul#102.