Add unlink clone checker. - Monitor changes of DOM-tree of the document - Unlinking a clone is actually removing the clone and copying nodes from the source. - Copy value of ID of a node to saved_id to track source of copy nodes. - For a new node with 'saved_id' is a copy of another node. - Copy vulae of 'saved_id' to 'ns0:duplicate-src' to keep the source - Change value of 'saved_id' to the value of ID of the node for later copying. - For a new node without 'saved_id' is not a copy of another node. - only set 'saved_id' to the value of its ID.