nodeview: allow users to place a node on an edge to automatically connect it

between the two nodes

UI convenience. Edge highlights when the cursor is in range to perform this
action.

app/widget/nodeview/nodeviewundo.h

@@ -36,6 +36,7 @@ private:
 class NodeEdgeRemoveCommand : public QUndoCommand {
 public:
   NodeEdgeRemoveCommand(NodeOutput* output, NodeInput* input, QUndoCommand* parent = nullptr);
+  NodeEdgeRemoveCommand(NodeEdgePtr edge, QUndoCommand* parent = nullptr);
 
   virtual void redo() override;
   virtual void undo() override;