zoom handling improvements

[bbondy]

zoom handling has a couple of problems:
i) We don't report the real percentage for the zoom in the hamburger menu. It should be consistent sizes reported as Chrome.
ii) We always zoom by equal 10% increments when at larger values this isn't useful and at smaller values it's too high. Zoom levels should be: 25, 33, 50, 67, 75, 90, 95, 100, 105, 110, 125, 150, 175, 200, 250, 300, 400, 500

[bbondy]

Fixed here:
04a47fd