[WIP] IPython Slide Viewer

Not ready to merge yet... but fully functional.

The related discussion lives in #52 issue.

The implementation is simple, I added reveal.js inside static folder and modified the app.py to call the SlideExporter instead of the HTMLExporter. Also, I have change the notebook.tpl to render the slideshow structure (as the reveal_slide.tpl inside nbconvert).

Cheers.