Implement the pretty homepage GUI

Summary

Prettified the login page and the home page.

Added Bootstrap, React Bootstrap and React Bootstrap Icons libraries
React Bootstrap is used for the "Log In" button on the login page and the "Browse Katsu clinical and phenotypic metadata" button on the home page
React Bootstrap Icons is used for the "Arrow in Box" symbol in the "Log In" button
Added DyCons logo and favicon in public folder
Added Header component that shows DyCons logo and title, and states "Researcher Portal"
Added Footer component that states that this is not to be used in production
Removed comment from App.js because App.js is essentially the starting point of the entire application and there shouldn't be a reason to state that

No dependencies on other PR's