Fix volume track position

- The volume track and thumb were not aligned. I'm not positive
  this is the best place to do this but it certainly looks better
  and this code definitely has the smell.
Fix assert generated in NSBezierPath

- For some reason we were getting NaNs in the rect it wanted
  us to draw into on my Retina test system. These NaNs would
  end up causing an assert when we use them to build an
  NSBezierPath. Now we just don't even try if we see one
  of those NaNs.
Enable Retina support

- There are lots of UI images that need @2x versions (pretty much
  everything) but this will at least get the video to use all
  the available pixels.