Make Domain Update more convinient

Assume you have a domain class User with a translatable property `description`. 
You update user details like this 

```
def update() {
   User user = User.get(params.id)
   user.properties = params
  user.save() 
}
```

If params contains a `lang` flag like `lang = en`. The `description` property in `UserTranslation` should be automatically updated. 
