[usability] When editing engines additional diagram window cannot be used for selecting trains

[prcek-prcek]

grafikon version

4.1.3 (Linux), run by ./bin/grafikon

issue

when editing any of engines, train units, engineers, circulation the diagram in the separate window is out of sync and cannot be used for selecting a train.

steps to reproduce

• create a net, define a route, put some trains in
• open addional window with the route diagram (View->Diagram), select route same as in the main window
• go to "Engines" tab, Create a new engine
• select a train in the main window, assign it to the engine
  • the train is grayed in the main window diagram, but not in the additional window diagram
• try to select a train by clicking into the diagram in the main window.
  • it can be selected, although it is not displayed in the diagram, selection is done in the list above
• try to select a train by clicking into the diagram in the additional window
  • it is highlighted, but nothing happens in the main window's list and train cannot be assigned to the engine as no selection is done

expected behavior

A diagram in the additional window behaves in the same way as the diagram in the main window. They're in sync even if routes aren't same and just overlap.