Refactor block to use functional components

[fului]

As the tendency of React and WordPress is to move towards functional components code, I suggest that the block is refactored to use this.

At the same time jQuery could be removed from the block code and instead rely on fetch and a couple of 3rd party libraries for TUS and Stream.

I have already started work on this, though I mistakenly deleted it all, so I started doing the work again.

I should also help make the code more structured and easier to maintain, in the long run, plus it should make it easier to implement testing, further down the line.

I would also be nice to use some of the built in components that Gutenberg supply, such as the MediaPlaceholder component, for giving a unified look to the block.

[fului]

I am already working on this and will hopefully have something ready shortly.

[B-Interactive]

I appreciate your efforts here @fului.

I agree less or no dependency on jQuery is a step in the right direction, as its need has declined.
Improved code structure, and using the WordPress built-ins also rings sensible, thank you.