UGENE crashs if a custom element is present in one WD window and was edited in another one

Scenario:

1. Open the WD.
2. Create an element with external tool and add it to the scene.
3. Open another WD window.
4. Edit parameters or slots of the created element (from the palette or add the element to the scene and then edit it).
5. Open the first WD window, click on the scene and on the element.
   Current result: UGENE crashes.

For now (in version 33) the issue should be solved as follows:
When an element with external tool is added to a scene of an opened WD window, but not the active WD window, on a user attempt to edit the element instead of the configuration wizard show a message box:

• Title: "Unable to Edit Element"
• Message:

  The element with external tool is used in other Workflow Designer window(s). Please remove these instances to be able to edit the element configuration.
  

• Buttons: "OK" and "Cancel".