Switch to using govuk_admin_template

* Start using admin gem which bundles jQuery, Bootstrap, environment indicator and default application layout
* Upgrade from Bootstrap 2 to Bootstrap 3
* Upgrade formtastic, formtastic-bootstrap
 * Switch from using deprecated `buttons` to using `actions`
* Update markup to conform with newest bootstrap patterns
  * Accordion pattern when editing an edition with parts becomes a set of rearrangeable panels
  * Same applies to edition history accordion
  * Replace grid classes on form elements with appropriate grid wrappers
  * Formtastic picks up most of the form changes, but for forms not using it:
    * Switch from `controls` to `form-group`, and ensure there's a `form-control` class on inputs
  * Add missing `-default` classes to default buttons and alerts
  * Use Bootstrap 3 kaminari themes for pagination
  * Update modal markup

![screen shot 2014-06-18 at 10 35 55](https://cloud.githubusercontent.com/assets/319055/3331042/2a29a2d6-f7d8-11e3-9a4f-51182848a2f3.png)

![screen shot 2014-06-19 at 18 39 06](https://cloud.githubusercontent.com/assets/319055/3331080/ab4947e0-f7d8-11e3-9d74-ca5272955860.png)