Update the About page and add a non-60fps warning on the front page.

Update the About page to suggest changing the display refresh frequency to 60fps
if comparing browsers.

Remove Focus from the list of subtests described.

Add the full list of 1.3 changes, linking to GitHub commits.

On the front page, if frame-rate detection detects a non-60fps rate, fix
the label below the Run button to suggest changing the display refresh rate.