feat: improves onDelete, dropzoneText and docs

[jpinho]

Description

This PR adds 3 contributions:

• New Feature (extension/non-breaking): Improving onDelete of the DropzoneArea to make it more useful
• New Feature (extension/non-breaking): Improving dropzoneText to make it more flexible
• Docs: Improving docs, killing the screenshots in favor of an animated GIF

How Has This Been Tested

All of the changes done here have been tested on a project consuming my fork version. Both onDelete and dropzoneText using react elements seem to work fine.

Checklist

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] New and existing unit tests pass locally with my changes
• [ ] Any dependent changes have been merged and published in downstream modules

[jpinho]

can you give this a look please @panz3r?

[jpinho]

Thanks for the review. I've seen it before, but just got from holidays. Will be addressing this the upcoming week.