perspective-viewer allows touch scroll and zoom events on mobile

[sc1f]

On mobile (iOS 11.4 + Safari & Chrome), perspective-viewer allows for touch zoom and scroll. These should be disabled.

• On Chrome, pinch-to-zoom is disabled but drag-and-drop causes scroll.
  

• On Safari, pinch-to-zoom and scroll are both enabled.
  

[sc1f]

Latest commit in branch responsive-sidebar fixes this using media queries and styling on body and html for viewports smaller than 600px. Safari ignores the user-scalable=no attribute and forces zoom on all pages, so we can't fix that part. Scrolling the body, however, has been removed.