Introduce answering questions in/after a demo to ITP, and to the Piscine demo rubric

Our trainees have improved a huge amount in how they give demos!

But, we often see that when our trainees are asked questions, they don't take time to fully understand them and target an answer well to them. They often answer a different question, or get stuck.

We should introduce practicing this into ITP, and assessing it into the Piscine.