scikit rebased (#170)
* Add structured classification validation
* Reduce diff
* Add sklearn structured-data-classification pipeline
* Add useful TODOs
* Add allowlist and change to cloudpickle
* Clean up common
* quality...
* WIP
* Change API contract for sklearn
* Add sklearn structured-data-classification pipeline
* Add useful TODOs
* Add allowlist and change to cloudpickle
* Fix broken merge
* Making last touches.
* Bad `self`.
* Bad rebase.
Co-authored-by: osanseviero <osanseviero@gmail.com>
