Impress improvements

A few impress improvements from trying to update the Pages deck...

* sniff slide ID from slide/section title for better permalinks
* remove generic title/description
* move header include to layout for simplicity
* w h i t e  s p a c e
* remove commented out code
* properly respect cover flag
* properly respect header flag
* strip demo css, add in bare bones structural css as standalone file

cc @jordanmccullough