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 
@burgvan Most of the pages are using sentence case (rather than title case) which is why I was suggesting using lowercase. So "Featured plugin: Lightbox gallery" would be consistent with the rest of the site.