Support touch events

[wyqydsyq]

Touch events on mobile aren't being captured by the underlying mouse-change package used by regl-camera.

Could potentially be solved by replacing use of mouse-change with https://interactjs.io/docs which abstracts click/touch and also supports gestures which would enable adding pinch to zoom on mobile

[MaxBittker]

took a crack at this, if you want to use my fork, point your package.json at
"regl-camera": "maxbittker/regl-camera",