Add videos for the Algorithms Challenges, and fix a few bugs in the challenges.
Commentary:
I think we have a decent spread of algorithms challenges now in the TS section (50 basic and 10 "challenges"). We may definitely revisit it with user feedback, but it will take a while to start getting user feedback on these - so this is a solid foundation in terms of getting people up to speed with the basics of writing code in my opinion.
This PR:
Commentary: