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 
Make sure to test any changes to colours to ensure they meet the minimum contrast ratio (4.5:1). A good tool for this is the [Colour Contrast Analyzer](http://www.paciellogroup.com/resources/contrastAnalyser).