Generate challenges.json

[Ethan-Arrowood]

Big PR right here. Going to update README.md after this for proper way to submit challenges.
Ref #8 #2

1. Challenge object within challenges.json now reflects chapter & lesson order (nested arrays).
2. Challenge directories with a lesson number > 9 will increment using the alphabet.
   Reason: due to an auto sort in fs.readdirSync('./challenges') when directories have double digits in the <lesson_number> portion of their name they are bumped up via the first digit (1 is followed by 10, then 11, then 12, then 2, 20, 21, 22, . . .). This creates a bug when generating the challenge list for challenges.json
3. Updated load-challenges.js to work with new challenges.json format (nested arrays).
   Also checks the last_edit date of the challenge.json against the localStorage challenge.json to verify integrity.

Some cool features included within generate-challenge-settings.js

• Will auto add new lessons [Not chapters yet]

• Will auto update existing challenges

• Uses included FS module of Node.js so can be executed using npm [will add]