Some definitions rely on others, in particular the c/cpp/c-like ones,
and we were appending the bundle of all files in the folder.
Instead for testing I've limited us to just three definitions. This has
the benefit of being a lot smaller to download/parse in test mode too.
Moves Highlight.js files to vendor/assets/javascripts
Adds Highlight.js in yarn package management
Removes old rake task and reliance on NPM to build Highlight.js
Highlight.js is now integrated in the "javascript:update" rake task
