Open the scenery editor from the start button's menu

eu07 -edit with the scenery file itself, not the export, so what is saved
lands in the scenery. Not every simulator build has the editor; that is said
before it starts.

StarterNG.Tests/StartSimulationTests.cs

@@ -95,6 +95,18 @@ public class StartSimulationTests
         Assert.Equal(new[] { "second", "third" }, start.SimulatorLogTail(2));
     }
 
+    [Fact]
+    public void The_editor_opens_the_scenery_itself_not_an_export()
+    {
+        var (start, launcher, installation) = Rig(files => files.WithExecutable(Build));
+
+        var result = start.ExecuteEditor();
+
+        Assert.Equal(SimulationStartOutcome.Started, result.Outcome);
+        Assert.Equal(new[] { "-edit", "td.scn" }, launcher.Arguments);
+        Assert.False(installation.Files.FileExists(TestInstallation.At("scenery", "$td.scn")));
+    }
+
     [Fact]
     public void A_file_that_cannot_be_run_is_not()
     {