UX clarifications:

• Clean all followers on search button click?
• What to do when the first username is equal to the second username?
• Will there be only desktop users?

TODOs/possible improvements:

• Handle too many common followers(pagination/infinite list?)
• Handle 403 properly(the internal lib just doesn't propagate it?)
• Improve time complexity of intersection algo
• Handle an edgecase with whispaces(only whitespaces/a username starts with a space)
• If the app is planned to have extended functionality, move things from App into the components folder
• Add end-to-end tests