Editor RAI tab

[JoanGi]

As a subsequent PR of the library adaptation for RAI attributes, this PR adds the RAI tab to the editor.

The tab follows the specification in http://mlcommons.org/croissant/RAI/ (near to be published)

There are also a few changes in the name of the serialize/deserialize function of the Python library.

After this PR, there is planned a PR to update some example datasets with RAI attributes