[cpp-qt5] client response headers and validation of properties for client and server (#1508)

* Add validation of required properties
Add Header extraction for client
* Remove some todos
* Add Test for Store API
Improve some checks for serialization

samples/client/petstore/cpp-qt5/PetStore/main.cpp

@@ -1,8 +1,10 @@
 #include <QCoreApplication>
 #include "PetApiTests.h"
+#include "StoreApiTests.h"
 
 int main(int argc, char *argv[]) {
     QCoreApplication a(argc, argv);
     PetApiTests::runTests();
+    StoreApiTests::runTests();
     return a.exec();
 }