(DO NOT CLONE) added adapted version of motivation.md that uses the pandoc slide generator and the new swc style

don't clone unless you know what you're doing (this commit will probably disappear)

Also modifed the Makefile to use the slides template for this file
instead of the generic template.

Note that we do not need a Markdown extension for deck.js because
Pandoc is doing Markdown-to-HTML conversion for us.