[RFC] Make work with dataset inheritances

I think, it isn't possible yet to do a data inheritance between data sets. 

Use case: 

You have an User with complex structure and you have to do a lot of duplicates for "basic" data. The solution is to create a base user data for re-usage. The other User data can inherit the data from this base data set. 

Example: 

```yaml
User: 
    base: 
        @abstract: true
        username: <username()>
        email: <email()>
        is_admin: 0

    admin: 
        @inherits: base
        is_admin: 1
```

What do you think?