MAINT: make DictXYElements XYElements

Summary

Refactor Converters and StructureElements.

You might want to merge !64 (merged) first.

Focus

As suggested in https://gitlab.com/caosdb/caosdb-crawler/-/issues/15

Note, that lots of changes are only renaming.

Test Environment

unit and integration tests

Check List for the Author

Please, prepare your MR for a review. Be sure to write a summary and a focus and create gitlab comments for the reviewer. They should guide the reviewer through the changes, explain your changes and also point out open questions. For further good practices have a look at our review guidelines

• All automated tests pass
• Reference related issues
• Up-to-date CHANGELOG.md (or not necessary)
• Annotations in code (Gitlab comments)
  • Intent of new code
  • Problems with old code
  • Why this implementation?

Check List for the Reviewer

• I understand the intent of this MR
• Check that no class changed in a way that changes the result that the crawler produces. If 'match' would not have forbidden, a continued used would have resulted in an application of the reg exp to another value than before (name instead of value). Such cases must be prevented.
• All automated tests pass
• Up-to-date CHANGELOG.md (or not necessary)
• The test environment setup works and the intended behavior is reproducible in the test environment
• In-code documentation and comments are up-to-date.
• Check: Are there specifications? Are they satisfied?
• If f-values was already merged, please merge into dev

For further good practices have a look at our review guidelines.