feat: `sector_classifications` gains `version` and `description` columns

Since all `*_classification` datasets now have a `description` column AND a `version` column (or `revision` in the case of `isic_classification`), we will be able to pass column out by the `sector_classifications` dataset. 

It should be noted that `cnb_classification` does not have a `version` column, but it will soon be deprecated.
This thus depends on #329 

Also depends on #344
