Google Prettify JS and CSS errors

[sk33lz]

I noticed some errors in the browser console due to the apparent fact that the JS include for Google Prettify is pointing to a dead project page. The bad JS file is hardcoded into the bottom of the base.html.twig template.

I've created a PR to fix this here, #17

Until that is merged...

• The new Code Prettify repo is located at https://github.com/google/code-prettify.
• The new JS file that needs to be used is located at https://cdn.rawgit.com/google/code-prettify/master/loader/run_prettify.js.