refactor css

refactor css and markup for better seo and page speed
- cleanup code
- refactoring
- scss implementation
- mobile-first support
- use variables for colors
- use shorthand
- better coding style
- grunt task for compiling and minifying
- reduce http-requests for faster loading time
- image optimization
- retina "form me" ribbon
- seo friendly markup
- wai-aria tags
- fix spacing
- combine css files

Change requests from 9 to 4 and file size from 35.6kb to 27.8kb
![homebrew-network](https://cloud.githubusercontent.com/assets/5244986/5531090/f87f9492-8a27-11e4-8a43-782dbb87d4bf.png)


Image diff screenshot with [wraith](https://github.com/BBC-News/wraith)
Minimal difference because of fixing a spacing bug and github ribbon not loading correction in phantom.js
![homebrew](https://cloud.githubusercontent.com/assets/5244986/5530925/20b8c21e-8a26-11e4-970e-f46aa5bde1ce.png)
I'm not a fan of splitting all the SCSS into separate files. Happy with SCSS but let's keep it in a single file.