ui: load project via MenuBar

This change adds a MenuBar to QtMainWindow and adds an action for opening a different project settings XML file. The
message MessageLoadProject is thereon used to load a new project in the Application and clearing the Storage.

src/app/main.cpp

@@ -12,7 +12,7 @@ int main(int argc, char *argv[])
 	QtGuiFactory guiFactory;
 
 	std::shared_ptr<Application> app = Application::create(&guiFactory);
-	app->loadProject();
+	app->loadProject("data/ProjectSettings.xml");
 
 	return qtApp.exec();
 }