transition to viewport units for scaling

[binford2k]

moving to css scale transitions across the board helped simplify the scaling algorithms, but it brought on its own weirdness. Let's figure out how to get away from scaling altogether.

If we define all font sizes in viewport units, then text should scale perfectly. Tables, callouts, etc. can all be styled that way. Eg, something like

.content h1 {
  font-size: 5vmin;
  font-size: 5vm;  /* for IE */
}

All that's left then is images that are not full-width. (Images that are full-width will also already scale perfectly due percentage width units.) If we have to scale them via javascript, we can probably repurpose the existing zoom() to just style all images within the slide content to a percent scaled width/height or the like.