Inserts a string into the list at the specified position, and associates it with an object.
Call InsertItem to insert the string S into the list at the position identified by Index, and associate it with the object AObject. If Index is 0, the string is inserted at the beginning of the list. If Index is 1, the string is put in the second position of the list, and so on.
InsertItem is the protected implementation of the InsertObject method.