Refactor jsFUNk to individual functions

[hfaerber]

Currently jsFUNk is set up with each function as a method on a larger object. This is consistently a point of confusion for students without enough learning or retained takeaways to be valuable struggle. Let's refactor the index.js file and the test file so that each function is stand alone, rather than a method on an object.

• Refactor index.js and test file to make the functions individual stand alone functions
• Revise README as needed
• Include the extra practice repo prompts (except object.keys prompts)
• Remove references to extra practice repo and ironFE across curriculum
• Re-record the video walkthrough of how to set up and use the repo, replace the existing outdated video walkthrough in the README

Note: you might think, maybe this is valuable for them to see! Especially since they use OOP and methods in Ruby! But in Heather's opinion, its not. Because their struggle with this formatting doesn't lead them to a clear understanding of that takeaway. Its wasted struggle because no learning around it is retained.