======Event_WindowClosed======
This event is sent to the plugin when a GRT main window is closed.

The event can be activated/deactivated in the plugin manifest.

===Values===
  * **//(integer) windowhandle//** - Windowhandle of the current GRT main window

===JSON source (example)===
<code>
{
  "Event_WindowClosed":{
    "windowhandle":531876
  }
}
</code>