Fix issue of shouting error when removing a node. - It shout a Python traceback message when removing a node that is referenced by a svg:use node. - when the node been removed, the node would be duplicated. The duplication was used to replace the svg:use one. - The ID of inserted duplication is the same as duplicated node, and modified to a new and unique ID. - Original design of domview_monitor can not handle it. - It is resolved by changing domview_monitor._id2node from single mapping to multiple mapping one.