Improve riddler markup

Problem/Motivation

The current riddler output has some flaws, we should discuss to address.

• Add captcha-riddler class to identify the captcha type
• Use other wrapper that "details" as collapsing an element
• Allow placing the question next to the answer by using CSS and a flexible DOM structure
• ...?

All issues which are inherited from CAPTCHA should of course be solved over there to not mix things up and keep consistency for all captcha types. So we'll have to check that first.

Finally we should check if CAPTCHA provides a twig file to allow clean overwrites as good as possible for forms.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes