Provide new question type: Vanilla

Answer entity is now field-able, which allow us create really flexible way to create new question types without code. Let's provide a vanilla question type, which is almost nothing, just a place holder, admin will add custom fields to question and answer bundles.

- Max-score is configurable
- Provide self-scoring features like quizz_text
- Admin can decide which field is used for answering form, which field is used for feedback form.