Bowerize HTML beautifier dependency

We either need to commit `beautify-html.js` to our repo or use bower to install it and grunt to move it to the right spot. We can't just do a symlink because that breaks our website build.

```
The page build failed with the following error:

The symbolic link `/src/test/unit/beautify-html.js` targets a file which does not exist within your site's repository. For more information, see https://help.github.com/articles/page-build-failed-symlink-does-not-exist-within-your-site-s-repository.
```