A grab bag of small changes to the cimbar.js web encoder UI:

• an error message is now displayed when webGL fails init (https://github.com/sz3/libcimbar/issues/95)
• toggling the menu now temporarily pauses the barcode animation for 15 frames (1 second)
  • this helps with autofocus issues on certain cameras
• on mobile, the touch event (press the screen anywhere) will also pause the animation
• a very exciting and mind-blowingly cool new background
  • ok, mostly I just rotated the grid by 45 degrees
• auto-expand canvas to fill window on larger displays (was previously capped to the cimbar res of 1024x1024 +padding).
• a larger minimum padding "dead zone" around the barcode

#97