fix(ios delegate) Eliminate crash on selector looking for "Window" (#6428)

* Add a "window" value so that NS doesn't crash on selectors looking for the delegate.window...

* chore: tslint

* chore: comments to referenced issues added

tns-core-modules/application/application.ios.ts

@@ -21,9 +21,20 @@ import { Frame, NavigationEntry } from "../ui/frame";
 import * as utils from "../utils/utils";
 import { profile, level as profilingLevel, Level } from "../profiling";
 
-class Responder extends UIResponder {
-    //
-}
+// NOTE: UIResponder with implementation of window - related to https://github.com/NativeScript/ios-runtime/issues/430 
+// TODO: Refactor the UIResponder to use Typescript extends when this issue is resolved:
+// https://github.com/NativeScript/ios-runtime/issues/1012
+var Responder = (<any>UIResponder).extend({
+    get window() {
+        return iosApp ? iosApp.window : undefined;
+    },
+    set window(setWindow) {
+        // NOOP
+    }
+}, {
+        protocols: [UIApplicationDelegate]
+    }
+);
 
 class NotificationObserver extends NSObject {
     private _onReceiveCallback: (notification: NSNotification) => void;
@@ -150,7 +161,7 @@ class IOSApplication implements IOSApplicationDefinition {
             this.setWindowContent(args.root);
         } else {
             this._window = UIApplication.sharedApplication.delegate.window;
-        }   
+        }
     }
 
     @profile
@@ -368,4 +379,4 @@ global.__onLiveSync = function () {
     }
 
     livesync();
-}
+}