Dragging doesn't work in popout windows
If you render a color picker in a pop out window, you cannot drag the color in that picker. See [here](https://codesandbox.io/s/react-color-in-popout-forked-nfx85?file=/index.js) for an example of this. This issue is present in both 2.18.1 and the latest 3.0 beta.

I suspect this is related to #357. I noticed that for example in Alpha.js and Hue.js the event listeners for mousemove are added to the window.

I was able to reproduce in Chrome, Edge and Firefox (all on Windows 10)