Proposes some updates to JS lessons 1 and 2.

These are some changes I think would be good for JavaScript lessons 1 and 2. I'd like them to initiate a discussion, and hopefully evolve a bit in the process. :)
This line has been edited, but there is still a question raised by this that may need more consideration. We show lots of loops with a knowable number of iterations. Should we add one with an unknowable number? This could be used to justify why we choose to use `while` loops sometimes. It may also be worth considering `break` and `continue` here.