[New feature] Make the use of graphs easier

Right now, it's relatively hard for a teacher to properly display graphs.
It may be helpful to have options for graphs in user-interface. Or maybe a specific problem type for graphs questions to avoid making the user interface heavier.

The issue names no files, tests, or entry points; start by locating the existing graph-display and problem-type user-interface code. Clarify whether the goal is graph-specific UI options or a dedicated graph question type, then define the chosen workflow and its completion criteria before implementation.

Rédigé par le modèle d'indexation à partir du texte de l'issue.