GitLab

* Refactor tutorial organization

* Merge tutorial subdirectoris under to examples/gallery/tutorials
* Do not use index.rst generated by Sphinx-gallery
* Instead use flat structure so that all the tutorials are listed in left menu
* Use `_assets` dir for artifacts of tutorials

fix 'file-does-not-end-in-newline' and typo.

Co-authored-by: krishnakalyan3 <skalyan@cloudera.com>

* Clean up extension build mechanism and extension location

* Add back the switch to depend on external sox

* Remove print

* Fix