Scripting: Have GTGUI.Server.GetElementByID() return nil when 'id' is nil.
Add event new event handlers in preparation for the new drag-and-drop system.
More foundation work for the new drag-and-drop system.
Add another drag-and-drop related event.
Another small addition to the drag-and-drop groundwork.
Add a scripting interface for the new drag-and-drop system.
Add the new drag-and-drop system and remove the old one.