Proposal: new structure for example pages

This proposal is for example pages to have a certain structure so they meet these requirements:

1. pages should only contain the HTML and CSS they, themselves need to display*
2. documentation about approach should be in comments in the CSS & HTML
3. SCSS partials should be single-purpose to satisfy point 1. & so their @import statements explain what they do

Note: point 1. is to help developers so when they inspect the CSS/HTML to see what is needed to make that pattern they aren't confused by code used somewhere else.