Add UI testing with Storybook

[xandervedder]

https://storybook.js.org/docs/writing-tests

[y-mpofu]

Hi! I'm a student in the CodePath AI301 program and I'd like to work on this issue if it hasn't been resolved yet. I'll start by reproducing the problem locally this week. Any pointers on where to start in the codebase would be appreciated!