Drag not working on mobile, scrolls the viewport instead

[lioneltay]

Dragging doesn't work on mobile since that is the gesture for scrolling on mobile.

[lioneltay]

Issue is that preventDefault needs to be called on the touchstart event to prevent the default scrolling behaviour while dragging.

Second issue is around Chrome defaulting document level event listeners to being passive (https://www.chromestatus.com/features/5093566007214080). Passive handlers cannot call preventDefault() as to improve scrolling performance by allowing the browser to know that scrolling will not be interrupted. React happens to bind its event handlers at the document level and then delegates the events to the appropriate handlers instead of attaching them directly to the node the listener was defined on (strange).

Solution is to get a ref of the draggable element and attach a touchstart listener manually which calls preventDefault() (look to cleaning this up in the future when react comes up with a solution facebook/react#8968