make it possible to create set app for GraphicsAppManager in deferred mode

examples/main.cpp

@@ -19,6 +19,8 @@ using namespace OpenVulkano;
 
 int main(int argc, char** argv)
 {
+	GraphicsAppManager manager;
+
 	std::vector<std::string> examples;
 	for (const auto& e : EXAMPLE_APPS)
 	{
@@ -36,8 +38,7 @@ int main(int argc, char** argv)
 	if (selectedExample >= examples.size()) throw std::runtime_error("Invalid menu selection!");
 
 	std::unique_ptr<IGraphicsApp> app( EXAMPLE_APPS[selectedExample].second() );
-
-	GraphicsAppManager manager(app.get());
+	manager.SetApp(app.get());
 	manager.Run();
 	return 0;
 }