Feature: Toggle difficulty of JavaScript solution code

[terichadbourne]

Recent lesson feedback shows that we have many users who are interested in tackling our coding challenges but fairly new to JavaScript and a bit put off by more advanced JavaScript tricks like powerful array methods that make the code more concise and elegant but are harder to understand than simpler and more verbose solutions like for loops.

Currently we're addressing this by:

• Adding hints with links to documentation for JavaScript methods they'll need
• Using some commented-out code in our solution so that we can present both easier and harder options for solving the problem

While not essential, it could be cool to offer a toggle of some sort that lets the user choose between seeing a beginner JavaScript versus an advanced JavaScript solution to each problem where this is relevant. This shouldn't affect validation at all since the result of the code would be identical.

There's a related issue in that we use the solution code from one lesson to inform the starter code for the next, and it's always tempting to use the advanced, more concise methods there to save space, so how this would interplay with the solution toggle is a potential complication.