[Python] Concepts naming cleanup and typo patrol

[BethanyG]

• Edited reference/README.md & exercises/README.md to change the class concept names and add numbers exercise.
• Edited list and list-method about.md docs for typos, code examples, and style
• Edited numbers about.md for better float type description/example.
• Edited Elyses Enchantments (lists) and Chaitanas Colossal Coaster (list-methods) to make them closer to the about.md docs in examples and style.