Front-end refresh: switch to govuk_admin_template

This is a complete front-end refresh, switching from bootstrap 2 to `govuk_admin_template`.

### Landing page
Before:

![image](https://cloud.githubusercontent.com/assets/23801/3091031/0bd801a0-e596-11e3-8396-ec2333e4a20c.png)

After:

![image](https://cloud.githubusercontent.com/assets/23801/3120593/323aaa46-e753-11e3-9e4e-30e27c77179c.png)

### New request list

![image](https://cloud.githubusercontent.com/assets/23801/3120599/51eb2ac8-e753-11e3-88a0-e8da0ac075b1.png)

### Content change request form

Before:

![image](https://cloud.githubusercontent.com/assets/23801/3091043/4a658d52-e596-11e3-8ae9-7d9fe3697d16.png)

After:

![image](https://cloud.githubusercontent.com/assets/23801/3120606/66767e02-e753-11e3-8b12-aa7932630ed1.png)

/cc @fofr