update complete Python chapter

[egpbos]

I have gone over the full Python chapter now and made some further updates (apart from those in #259, #260, #261 and #262):

• updated documentation section to recommend sphinx only (removed pydoc)
• removed jupyterlab "under development" caveat, it's mature now
• added ReviewNB suggestion based on good experiences in a number of projects
• add some minor textual changes

[egpbos]

Note to reviewer: the link checker is failing because of dead links in master. We should make a separate PR to fix them.

[egpbos]

Thanks for the review! Added your suggestions.

[c-martinez]

Thanks for updates in this chapter!