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 
This doesn't make sense as an h2. If it will be on the same page as "I want to fix or improve WET as a developer" then it should probably be a sub-section of that section.