Allow 'fundamentals' sample page to create its own codepens

Objective:

- Allow us to insert our own markdown or html between codepens

As part of this work I have:

- Update the config file, to move away from a deprecated setting
- Brought the codepen html generation out to an includes file
- Updated codepens in 'fundamentals' page to be taken out of then Front Matter

Tested with `jekyll serve` on a Linux desktop (Ubuntu 14.04)