Adding slides

Adds templates and example for creating motivational slide deck using [deck.js](http://imakewebthings.com/deck.js/) (which seems a lot cleaner than reveal.js).

* Updating `pages/motivation.md` to use the right template and have the right content.  (Can't avoid using HTML tags for sections...)
* Update `Makefile` to use the right template for the slides (instead of the generic template).
* Create the template for slides.
* Add all the support files needed by `deck.js`.

To do: update `README.md` to describe these changes.