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, remove old bootstrap assets that weren't coming from gem
* Update chosen library
  * Style chosen selects to match bootstrap 3
* Update markup to conform with newest bootstrap patterns
  * Add bootstrap 3 classes to form elements
  * Update bootstrap grid classes
  * Replace grid classes on form elements with grid wrappers (you can't apply grid classes directly to forms in bootstrap 3)
  * Add missing `-default` classes to default buttons and alerts
  * Use Bootstrap 3 kaminari and alphabetical_paginate themes
    * Patch alphabetical_paginate gem which has some broken HTML
  * Stop nesting tables in wells
  * Give table headers contrast
* Add simple breadcrumbs to appropriate pages
* Remove a lot of the custom signon CSS that was overriding default bootstrap behaviour
* Tweak behaviour of password change form based on limitations of bootstrap 3 add-ons — add-ons can't be toggled, so an indicator is always shown, but it begins greyed out.

![screen shot 2014-06-26 at 15 16 25](https://cloud.githubusercontent.com/assets/319055/3444376/ebdbf196-012d-11e4-9716-04327517bfa2.png)
![screen shot 2014-06-26 at 15 16 50](https://cloud.githubusercontent.com/assets/319055/3444375/ebdb7072-012d-11e4-9270-015d02289085.png)
![screen shot 2014-06-27 at 11 24 24](https://cloud.githubusercontent.com/assets/319055/3444377/ebdda87e-012d-11e4-8c86-547cb4940548.png)
![screen shot 2014-06-27 at 18 23 00](https://cloud.githubusercontent.com/assets/319055/3444378/ebddbcb0-012d-11e4-9350-c3414102cb0c.png)
![screen shot 2014-06-27 at 18 23 16](https://cloud.githubusercontent.com/assets/319055/3444379/ebde0652-012d-11e4-86a1-7d735346c069.png)