Changing properties of service groups after creation

Currently, once you create a service group all properties are fixed. You have to re-create the service group if you want to change something. This is problematic especially for service groups, where you want to add/remove/update services or domains after creation because it means you also have to re-create the instances. Furthermore, you cannot avoid a downtime in this case.

It should thus be possible to change settings of service groups without having to re-create the group.