[escher] Add methods viewWillAppear/Disappear in view controller instead

of keeping track of dataHasChanged in the selectable table view

Change-Id: Id2626f527f44714e29b9bd66e2c843193e1b57b5

escher/src/view_controller.cpp

@@ -8,3 +8,9 @@ ViewController::ViewController(Responder * parentResponder) :
 const char * ViewController::title() const {
   return nullptr;
 }
+
+void ViewController::viewWillAppear() {
+}
+
+void ViewController::viewWillDisappear() {
+}