Fix mousemove bug

onmousemove function does not attach mousemove event handler to html dom
element because mousemove event is not whitelisted in dom-delegator library.
See

https://github.com/Raynos/dom-delegator/blob/master/index.js#L10-L16

According to docs

https://github.com/Raynos/mercury/blob/master/docs/life-cycles.md#reacting-to-dom-events

we should call delegator.listenTo('mousemove') to fix this issue.