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 
The background, border and link colour (normal and hover) are all the same colour. This will make the menu bar into one solid colour with no visible links or anything (even on hover). The link and border colours should be different than the background colour. Also there should be a hover/focus effect of some sort so users actually know the menu is active.