Add new Getting Started page

Modified content in start-en.hbs to match the new theme, 
Added page specific css in content/_base,scss
Modified colours in main/_base.scss and footer/_base.scss
Modified link colours in _variables.scss 
My point was more about rolling out the changes page by page with targeted CSS. We will eventually get to changing all pages but should avoid global changes like this so we don't end up with an awkward partially changed state. This would only be a temporary approach until everything gets changed over and tested.