Add videos to relevant JavaScript Core insights

[lizTheDeveloper]

We're going to incorporate video content in Enki soon, but we're going to maintain our commitment to using free, open-source materials. This guy makes amazing JavaScript videos that go over fundamental JavaScript concepts. https://www.youtube.com/channel/UCO1cgjhGzsSYb1rsB4bFe4Q

Attach as many of his videos as you can to as many JavaScript insights as are relevant. Do this by adding a link to the links field, formatted like so:

• 'Higher-order functions Video{video}'