cmd/present: Fixed printing of slides.

I moved print.css into styles.css - to make it obvious that it needs to be
considered when modifying the styles.css. I use @media screen for all the
framwork related css, this means the @media print doesn't have to start
overriding each property - also there's less chance of a problem when
something isn't overridden.

Change-Id: Ic58e8c80df3339b55f67140a47866a232e0d30a3
Reviewed-on: https://go-review.googlesource.com/5526
Reviewed-by: Andrew Gerrand <adg@golang.org>
3 files changed