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 What they were referring to was using <code>section</code> just for styling content instead of for it's intended purpose which is document semantics. It is bad to use any semantic element for styling purposes where it is also not used for semantic purposes. In this case you are using it for semantic purposes first then applying CSS to it to style it as well. That is acceptable and actually encouraged since we don't want to use unnecessary elements and bloat the page.