Fix LTR end to end notebook (Fixes 100)

[softwaredoug]

Saves the product judgments file, and other fixes to the ch 11 end to end notebook

[treygrainger]

@softwaredoug I'm still getting a failure reading the product_judgements file. Does it need to be committed here?: https://github.com/ai-powered-search/retrotech

[softwaredoug]

Let me do a clean rebuild again, but the file should be written on this cell:

judgments_to_file(open('data/product_judgments.txt', 'w'), judgments)