Implement #545

* Instance group can be selected when creating and copying instances
* Original group is pre-selected when copying
* Last used group is pre-selected when creating new instances

MultiMC.cpp

@@ -376,6 +376,9 @@ void MultiMC::initGlobalSettings()
 	// Notifications
 	m_settings->registerSetting("ShownNotifications", QString());
 
+	// Remembered state
+	m_settings->registerSetting("LastUsedGroupForNewInstance", QString());
+
 	// FTB
 	m_settings->registerSetting("TrackFTBInstances", false);
 	QString ftbDataDefault;