#2 drag and drop event - change handles

[Michael Davey]

When dragging the start of an event, the drop is ignored if it is on a later day. Similarly, when dragging the end of an event, the drop is ignored if it is on an earlier day.

It would be nice if the drag handle swapped between start-handle and end-handle depending upon whether the handle is currently hovering over a day in the future or in the past.