New Feedback button and amall UX improvements

I want to be more active sharing the progress on how are we building courses there is a small update:

• We improved how students leave feedback, first students mark lesson as completed and then some emojis ( 😭 🥱 😐 😀 😍 🤯) appear to ask for the feedback.
• We are now supporting using the cover image from notion and improved the course landing pages a little bit.