Allow ref forwarding

[andfk]

Hi! Thanks for the component, it is very helpful but i have hit a limitation as i needed to call the onImageRemoveAll from a hook function. I could have by passed such method from the render itself but i don't like the approach and thats why i've implemented the ability to use a ref and expose the same methods offered in render.

If you accept this PR please consider the React docs advice in order to bump the release version.