[FEATURE] refactor api entities with entity wrapper classes

__Tasks:__

- [x] gather feedback for my changes
- [ ] submit changes to the documentation


__Informations:__

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| Tests pass?   | yes
| Fixed tickets | none
| Doc           | none
@alexander-schranz Maybe it would be a good idea to just pass the id, and let the exception generate the message (should be pretty much the same everytime)