Switch to using govuk_admin_template

Recommend reviewing code using`?w=1`, and doing like-for-like comparisons with preview.

* Start using admin gem which bundles jQuery, Bootstrap, environment indicator and default application layout
* Switch from LESS to SASS
* Upgrade from Bootstrap 2 to Bootstrap 3
* Upgrade formtastic, formtastic-bootstrap
  * Update deprecated formtastic actions
* Update markup to conform with newest bootstrap patterns
  * Replace grid classes on form elements with appropriate grid wrappers
  * Formtastic picks up most of the form changes
  * Add missing `-default` classes to default buttons and alerts
  * Use Bootstrap 3 kaminari themes for pagination
* Update flash messages for new Bootstrap 3 alerts
* Make services table more useful
* Bring guidance on file uploads inline with content style guide

Before:
![screen shot 2014-08-28 at 18 18 29](https://cloud.githubusercontent.com/assets/319055/4088821/a03d18ba-2f62-11e4-84a2-55a26a45d1f0.png)
![screen shot 2014-08-29 at 11 01 10](https://cloud.githubusercontent.com/assets/319055/4088874/764fc858-2f63-11e4-85b6-6ccb09dc4501.png)

After:
![screen shot 2014-08-28 at 18 18 10](https://cloud.githubusercontent.com/assets/319055/4088822/a49c3d96-2f62-11e4-8283-36a38c9eb46d.png)
![screen shot 2014-08-29 at 11 00 47](https://cloud.githubusercontent.com/assets/319055/4088879/7f189230-2f63-11e4-874c-75b48b3848a7.png)
![screen shot 2014-08-29 at 11 00 16](https://cloud.githubusercontent.com/assets/319055/4088883/9027cb86-2f63-11e4-8285-43a9aabedc2d.png)
![screen shot 2014-08-29 at 11 00 29](https://cloud.githubusercontent.com/assets/319055/4088884/902eff1e-2f63-11e4-8b15-3db96a60a5a9.png)