Full-finger gesture control on touch-screen devices

Other notable fixes and improvements:

1. Fixed canceling full-screen view while loading high-res images in full-screen.
2. Fixed full-screen button that was partially visible in zoom_light and zoom_dark skins when inside iFrames.
3. Improved stability of 360 spinning on page scroll when page scroll is configured without smoothing.
4. Fixed "play to label" automation when play speed was set to 0.
5. Fixed API property disableRelativeAssets that didn't work in full-screen.
6. Added API property externalImages for overriding images in XML config:

[
  {
    image: "https://your-image-server/1.png",
    zoomImage: "https://your-image-server/1-large.png" // optional
  },
]