Backend of our CLI dev challange.

The server exposes the following endpoints:

• GET: /challenge/${challenge}/data.js - data endpoint for each challenge
• GET: /challenge/${challenge}.js - static endpoint for front.js
• POST: /check - checks the answer for a specific challenge. Returns with the keyword and the name of the next task if answer was correct or an error with a custom message otherwise.
• GET: /jumpTo - jumps to the task after the one which is identified by the keyword provided