Improve quiz generation

[Romern]

See #54

[septatrix]

This should be possible by using the mod_quiz webservices. Maybe just generating a clean HTML from them with embedded mathjax is sufficient?

[n0toose]

Which are the criteria for this issue to be considered as complete?

[septatrix]

Preferably wkhtmltopdf should not have a fixed delay but instead wait until MathJax is finished. This would require injecting some js into the page.

Alternatively Quizzes may be rendered manually using e.g. Latex but that seems even more cumbersome.