Merge branch 'f-select-subproperties' into 'dev'

f-select-subproperties -> dev

# Summary

See summary of https://gitlab.com/caosdb/caosdb-webui/-/merge_requests/72

Funny side note: this MR !47 and the issue it resolves #47 have the same number  

# Focus

* The important changes are in `RetrieveFullEntity.java`, `EntityToElementStrategy.java` and `SetFieldStrategy.java`.
  * `RetrieveFullEntity.java` is responsible for the retrieval of entities and it needed additional functionality to retrieve referenced entities recursively. It does this but only if a list of `Query.Selects` is there and non-empty, because this is the case when the request is a SELECT query.
  * `EntityToElementStrategy.java` is responsible for the xml generation. It was kind of buggy and I did some refactoring there.
  * `SetFieldStrategy.java` is decides whether a property of an entity is to be included in the generated output (xml) or not. 
Additional functionality is added to cope with deeply nested references.
* Note: I also deleted the AWI stuff, because I didn't want to refactor these classes.

# Test Environment

See https://gitlab.com/caosdb/caosdb-webui/-/merge_requests/72

# Check List for the Author

- [x] All automated tests pass
- [x] Reference related Issues
- [x] Up-to-date CHANGELOG.md
- [x] Annotations in code (Gitlab comments)
  - Intent of new code
  - Problems with old code
  - Why this implementation?


# Check List for the Reviewer


- [x] I understand the intent of this MR
- [x] All automated tests pass
- [x] Up-to-date CHANGELOG.md
- [ ] The test environment setup works and the intended behavior is
  reproducible in the test environment
- [x] In-code documentation and comments are up-to-date.
- [ ] Check: Are there spezifications? Are they satisfied?

For further good practices have a look at [our review guidelines](https://gitlab.com/caosdb/caosdb/-/blob/dev/REVIEW_GUIDELINES.md).

See merge request caosdb/caosdb-server!47