Move cookie message above header

This prevents the situation where the cookie message, new phase banner and
survey compete for attention under the header. 

The cookie message appears once at the top, moving the content beneath it down.

Screenshots:

![gov uk - cookie message - mobile](https://cloud.githubusercontent.com/assets/417754/2956546/b9893248-da91-11e3-86f4-6c223037c78f.png)

![gov uk - cookie message - desktop](https://cloud.githubusercontent.com/assets/417754/2956548/be0b8eec-da91-11e3-9894-41d57030b9af.png)