Support to drop callback (jquery.jOrgChart.js)

[wesleypimentel]

As we speak, here is the inclusion of support for callback functions on the event drop as user review @deJong-IT in https://github.com/wesnolte/jOrgChart/issues/25#issuecomment-11480187. I hope it's satisfactory. In resume, if option dragAndDrop is set a function, the callback runs. Note: In use, the solution worked well. But I noticed a certain delay between the drop event and the redraw of the chart, so I was forced to use a temporary timeout in my handler function, until find a better solution. I take this opportunity to thank you for consideration and commend his excellent work with the script. Congratulations!