Issue #2395311: Clean up quiz form

https://www.drupal.org/node/2395311

<h3 id="summary-problem-motivation">Problem/Motivation</h3>

Quiz form definition is now quite mess. Admin can not control weight of elements. There's quite much hack over there.

<h3 id="summary-proposed-resolution">Proposed resolution</h3>

- Make sure title is displayed before body field.
- Move extra fields definition to entity (extra fields) controller.
- Admin can control weight of element, tabs, …
- Require field_group.module