Extend safety of scripting api decorators

The scripting api decorators (.title, .id) operate only on some fields and there are no guarantees that we have no duplicated handling (=two decorators delivering two values that we'd need to combine). The handling is currently quite naive - select first accepting the field and decorator, return its decorated value, ignore the rest. We should be able to handle these situations better, maybe recognize error conditions during compile or startup time already and make the handling more robust.