[orx-gui] Add <T: Any> T.addTo(WindowedGui)

orx-jvm/orx-gui/src/main/kotlin/WindowedGUI.kt

@@ -61,4 +61,10 @@ class WindowedGUI(
             cw.program.extend(gui)
         }
     }
-}
+}
+
+@JvmName("addToWindowedGui")
+fun <T : Any> T.addTo(gui: WindowedGUI, label: String? = this.title()): T {
+    gui.add(this, label)
+    return this
+}