Update SwatchJS drop and update tests

- Get latest source drop of SwatchJS (overwriting old colorHelper)
- Comment out the base64 comparisons in tests. Each browser comes up with
  a different encoding which raises false failures
Refactor diff algorithm and performance improvements

- Turn on strict mode
- Rename .diff2() to .startDiff()
- reduce # of locals
- Replace .forEach() calls with .map() to clean things up
- Extract .returnOutput() from .startDiff() so it takes all its inputs as
  paramters and doesn't rely on closure variables
- Made ctxDiff local to .startDiff() instead of being in the .diff()
  closure
- Elminated canvasDiff variable
- Avoid repeated calls to canvas's .data member for a nice performance win