Feature: Hint for Well-formed-formulas [WIP]

[malikpiara]

Hi! Issue #49 made me rethink how feedback is given within a Quiz and I decided to both improve the feedback system and handle feedback related with well-formed formulas differently.

Instead of reminding the learner what constitutes a well-formed formula for the question if they get it wrong, we're going to display a hint that learners can always access as they're going through the exercises. Here's an inicial look:

Improving Feedback System 🌟 - Watch Video

Thank you @rabuf @mnba and @cwgreene for your kind feedback, as well as @LinusBolls for helping refactor the logic of how feedback is given within the quiz. Please feel free to share your thoughts so we can incorporate them in the next release!