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 
You can control the size with the h1, h2, h3, h4, h5 and h6 classes (but should be careful to not make a heading look not like a heading). HTML now allows headings in summary tags as well (changed a couple of months ago). It is possible that our HTMLlint hasn't caught up to that yet.

Either way the heading structure needs to be correct first, then the visuals need to be corrected as needed.