Add OnScriptMovingStartEvent and OnScriptMovingEndEvent to EventManager so that these can be triggered by future code (not yet implemented).

Also hooks up moving_start and moving_end script events, eliminating itemID on XEngine EventManager methods since this is completely unused.
An adaptation of the patch in http://opensimulator.org/mantis/view.php?id=6515
Thanks Garmin Kawaguichi and Signpost Marv.