Add Financial Times branding and deeper header

/cc @matthew-andrews @wheresrhys 

![branding](https://cloud.githubusercontent.com/assets/1978880/5246653/44c79eec-7963-11e4-83bb-7917bb83fef6.gif)

- Add Financial Times logo for largish screens
- Make header slightly deeper
- Set homepage link to be "/" rather than "next.ft.com"