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 
@pjackson28 I believe we'll be having the blue background and white text for all H1s on every page to keep it consistent rather than having that visual treatment on only a select few. Would this be an issue? Would you suggest it'd be easier to also include the "page description" under the H1 as a conditional?