Add functionality to only syntax-highlight codeblocks

[kylecesmat]

Right now, we are using Codemirror to parse markdown and return playgrounds for specified codeblocks. I think it would make sense to introduce functionality that syntax-highlights all other codeblocks. This would allow the developer to only use one library/theme for code-previews.

I'm not sure if Codemirror has the ability to disable editing & only highlight the markup, or what the performance cost of that would be. It would likely make the most sense to use Codemirror for this rather than including another library like Prism.