Add Hugging Face demo, SKLearn challenge

[athewsey]

Issue #, if available: N/A

Description of changes:

• Merge different framework versions under exercise-wise folders, instead of separating out pytorch_alternatives
• Add new script mode demo variant for Hugging Face (still NLP)
• Add new migration challenge option for Scikit-Learn, for participants less familiar with DL (inspired by the ANZ SageMaker immersion day)
• Update DataSci and PyTorch kernel versions
• Downgrade ipycanvas widget to work around this issue
• Point notebooks to us-east-1 notebook metadata so users should avoid kernel selection prompts when deploying in this popular region.

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