New Getting Started page

@thomasgohard 
Here is the new Getting Started along with edits I made based on some of Paul's comments in the old pull request. I also edited the background for the breadcrumbs which I forgot to do in the menu-footer-colours pull request. Now the background is white to follow with the rest of the white background of the site. 


@thomasgohard We did think of that before in the process of re-designing this page, but we thought it would probably be overwhelming for a new user who's just starting to get familiar with WET which is who we're targeting. The list of all polyfills and plugins is what the Working Examples page is for - a page for experienced developers who already know how to use WET. With this new design, we are trying to help novice users to understand what a polyfill does. I hope this makes sense.