[Escher] Responder can get a pointer to the parent App

We assume the root parent is the App. This works well because each view
controller is a Responder.

Change-Id: I5d90053949a4ffbdb78746cc85430a15138e48e7

escher/src/view_controller.cpp

@@ -1,7 +1,8 @@
 #include <escher/view_controller.h>
 
-ViewController::ViewController() :
-  Responder() {
+ViewController::ViewController(Responder * parentResponder) :
+  Responder(parentResponder)
+{
 }
 
 const char * ViewController::title() const {