Improve rendering in IE7

* Travel Advice Publisher doesn't have many users, but a significant proportion of them use IE7.
* Give better support to IE7 users by pulling in the latest admin gem fixes (https://github.com/alphagov/govuk_admin_template/pull/29)
* Use input helper classes so that form fields are shorter in width when a page is linearised (as it is in IE7)

Before:
![screen shot 2014-07-03 at 13 10 07](https://cloud.githubusercontent.com/assets/319055/3469217/167b8f50-02ab-11e4-92c8-8417b694f497.png)

After
![screen shot 2014-07-04 at 17 17 29](https://cloud.githubusercontent.com/assets/319055/3483817/0b79c36e-0397-11e4-9c8b-de3c5912d781.png)