revealjs: backport hakimel/reveal.js@08fb6cb2f96a6d97aaa21c35a925ebb59b0b0070 to fix printing in Chrome 33 (hakimel/reveal.js#808)

The fix involves removing the media definition of print on pdf.css, ie.
applying pdf.css in a blanket fashion, so pdf.css has to be inserted via
JavaScript (when ?print-pdf is in the url). Hence the JavaScript.