Attaching a screenshot of how the overlay should look like.

- The list of groups to delete should be in a well, very similar to how the manageaccess widget does it
- The `Are you sure` question should be a standard title
- Underneath the list of groups to leave, a `alert alert-danger` div should be shown with the text `Caution: This action cannot be undone`
- The action button should be of the `btn-danger` type

![screen shot 2013-05-27 at 11 08 37](https://f.cloud.github.com/assets/109850/567425/bb8731e4-c6b5-11e2-90a8-39690a2536c8.png)