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 
Yes, otherwise anything else is not allowed to be in summary. I tried using h2 and a div to make changes within the summary element, but they didn't pass the HTML validation test.