Added ability to delay destroying of highcharts for animations.

[ErwanLent]

I've added the ability to delay destroying of highcharts to let animations finish without a memory leak.

[ErwanLent]

I've found a solution. chart.destroy() needs to be called for there to be no memory leak. However, if you wait a delay inside the beforeDestroy event, this.chart becomes null and you cannot call destroy() on it. Highcharts, however, saves all the charts globally in Highcharts.charts. If you store the chart id in beforeDestroy, wait a delay for a transition to finish, then call the destroy() function on the chart stored in the Highcharts.charts array, the problem is solved.

I've forked the repo and added a destroyDelay prop that gives the option of putting in a millisecond amount before the highcharts is destroyed. I've run the build process, forked the repo, and opened a pull request. Please feel free to change the prop name.

Fix can be played with here: https://jsfiddle.net/hpkoemtw/2/