Switch to use core-layout wrapper

- Use the core layout wrapper
- Indent code-blocks and examples in to the same reading edge as the
  content.
- Add styling for headings and paragraphs used used on the component
  pages, using the core layout resets everything so they need some sizes
  adding back
- Use direct decedent selectors for tag based selectors so they don't
  effect the examples
- Add swap out encoded new lines from fixture data to actual new-lines
Could you put this in the `Component` model instead? eg `@component.html_body`?