Convert to static GitHub pages

[Gerg]

Running version: https://gerg.github.io/cf-onboarding/

This should be to gh-pages branch, but you can't create PRs to new branches.

• With the demise of Pivotal Tracker, there needs to be a new way to organize and display the onboarding content
• Inspired by https://github.com/cloudfoundry/cf-networking-onboarding
• For now, this is a mostly direct port of the content to markdown files, without modifying it to reflect the new format (e.g. there are still plenty of in-text references to "Tracker")
• Initialize a new Jekyll site to run on GitHub pages
• Remove converted .prolific files