Update glossary
This PR adds some more computer vision and speech terms (feel free to suggest more!) and reorganizes it alphabetically (and each term can be linked to) so it's more like an actual glossary. I also edited some of the terms, like `attention mask` for length, since a glossary typically just provides a brief definition. If we want to keep the explanations, maybe I can link to the course instead.
I cannot review this PR as it is. You have changed the text for the existing entries and removed the links to the YouTube videos and since you did it with the reorganization, the diff makes it impossible to properly comment.
You have also removed existing entries like autoencoder model or autoregressive model.

Please focus on one thing at a time per PR (I have already told you this multiple times). For instance here, focus first on the reorg **with no other changes in existing content** and then in a second PR we can discuss text changes.<|||||>Sorry, I'll try to slow down and just focus on one thing at a time!

I'll close this PR and open two separate ones to address the reorganization and new terms.