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 
Steps should be put in an ordered list (<code>ol</code>). If it is necessary to keep the step number in the summary then at least use an unordered list (<code>ul</code>) to give some semantics. Can hide bullets with <code>class="list-unstyled"</code> if necessary.