MD Style additional predefined custom containers

[utetrapp]

User Story

As a: teacher

I want: to have custom containers within the md unit for hints etc.

so that: I can format my md units nicely.

Acceptance criteria:

• [ ] container for learning objectives
• [ ] container for hints
• [ ] container for assignment
• [ ] container for question
• [ ] container for example
• [ ] container for todo

Additional info: