Working code for handling PDFs.
PluginLoader overrides the PluginLoader in webodf with an extra entry
for PDF files, and that's all.

During building, the built viewer/ directory is copied from webodf to
Viewer.js's build tree, and PluginLoader is overwritten with Viewer.js's
copy.
Package up everything into a nice zip
Treat it as a slideshow if the width is greater than the height of the
page
Firefox needs -moz-selection prefixed css
Merge pull request #1 from adityab/master

Working implementation of PDF.js backend