If we want to save more data in the version-object, we should append the version class. I don't like the possibility of two identicly versions. It has the risk, that someone wants to write the data in a new version, but sets some other attributes before, for example in this case

```python
version = motion.new_version 
motion.identifier = 'foobar'
motion.save()  # the coder thinks he only saves the identifier
motion.title='new title'
motion.save()
```