Implement in memory the data structure "graph" and a graphical interface for editing it. User manual: 1)lclick+ctrl == add node; 2)lclick+alt == delete node; 3)rclick+ctrl == add edge (you need click on node_1(it will be highlighted in color) then repeat operation for another node_2); 4)rclick+alt == delete edge (you need click on node_1(it will be highlighted in color) then repeat operation for another node_2);