Resolve "Re-design smileys on TA feedback"

What does this MR do?

Smileys in feedback for TAs are redesigned:

• buttons are color-coded (in a way indicated in the #291 (closed) issue description)
• buttons and smileys are larger for better visibility

Smiley button group design

Normal view

Hover-over view (on the angry, red smiley)

Does this MR meet the acceptance criteria?

• I have added a changelog entry to reflect the significant changes I made. (not needed - only UI was changed)
• Tests were created to test the feature. (not needed - only UI was changed)
• I have updated the documentation accordingly. (not needed - only UI was changed)
• I adhere to the style guide.