Add tips to exercises

[pdawyndt]

From Brecht Willems (brecht.willems@ugent.be):

De mogelijkheid toevoegen om tips/hints toe te voegen aan de opgave, die pas weergegeven worden als de gebruiker klikt op de titel van de tip/hint. Op die manier kunnen studenten, wanneer ze daar nood aan hebben, een extra tip/hint krijgen voor die opgave

Original issue by @pdawyndt on Thu Apr 25 2019 at 18:50.

[pdawyndt]

Some reflections:

• in programming courses, we also use tips (title + description) for exercises that we now bundle in a PDF that is linked to a course series; would also seem like an improvement if we could have Dodona-support to provide these tips directly from the exercise; we also reuse these tips in multiple exercises; could be an idea to put tips in an exercises repo and find a way to link tips to exercises
• from meeting with Dries Benoit: DataCamp apparently also support tips and tracks which users have used the tips (as feedback to the instructors/teachers)

Original comment by @pdawyndt on Thu Apr 25 2019 at 18:54.

[BTWS2]

For now I use this in the exercise description.

Tip (Click here to expand)

This is a useful hint.

<details>
  <summary>Tip (Click <b>here</b> to expand)</summary>
  This is a useful hint.
</details>