Redesign quiz from scratch

[Privat33r-dev]

Fixes #258

Still WIP, but is ready to use. Points to address:

• Resolve situation with checkboxes: I need label to be big so when users clicks, checkboxes is also toggled; when I make checkbox inside of the label, CSS properties (e.g. to make text bold when checked) don't work through "~" operator. In theory, I can resolve with click event on JS, but it feels a bit dirty. For now I just made them invisible, but UI is somewhat sufficient.
• Explain to user that he got the question correct/wrong.
• Count total points received by user.
• Submit text answer on Enter
• Add alternative variants for open ended questions. Can be achieved by regex.
• Limit styling only to the article to avoid design issues in other parts (bootstrap, jquery removal update in different PR)

UI Preview

[Privat33r-dev]

@marcosnils I want your input on this PR :)

1. Would it be acceptable to use regex as input for the answer by MD authors? Example: (docker )?(ps|container ls)
2. Where it would be the most appropriate to output the quiz result?
3. What would be the appropriate syntax for the question's explanation? (explanation is essential part of the quiz, since it help to provide insight on missed topic)
4. How can we explain that question was correct/wrong? Some users are colorblind, so it might make sense to use icons for this in the container below(?) the question. Also visual cues might be useful part of feedback, maybe ✅ for correct and ❌ for the wrong ones on the right side?

[Privat33r-dev]

@marcosnils hi! I want to follow up on this PR. It would be nice if you can find some time to provide response for the questions above so the PR can be improved. Even in its current state, it can be considered as ready to merge and improvements can follow in subsequent PRs.

[Privat33r-dev]

@marcosnils hi! Any interest in reviewing this one? :)