Refactor Class Components to Functional Components

[palagdan]

Functional components are recommended for better performance and simplicity. They also provides hooks and are better for understanding of the component life cycle.

[blcham]

I consider it a low priority unless it brings some concrete value. We should refactor specific class components --> functional components when fixing issues/providing new features within the context of the issue.

This can be done incrementally or in combination with #97.

[blcham]

@palagdan