An ordered list of EdgeEndBundles around a RelateNode. They are maintained in CCW order (starting with the positive x-axis) around the node for efficient lookup and topology building.
Insert a EdgeEnd in order in the list. If there is an existing EdgeStubBundle which is parallel, the EdgeEnd is added to the bundle. Otherwise, a new EdgeEndBundle is created to contain the EdgeEnd.
Update the IM with the contribution for the EdgeStubs around the node.