Allow to override aria-label for full screen button and thumbnails

[leandrocrs]

Is your feature request related to a problem? Please describe.
We are using this component in a Brazilian Portuguese application, where some users lay on screen readers to navigate through application, and for our surprise we cannot override the Fullscreen button and thumbnails aria-labels to match our language.

Describe the solution you'd like
Allow to override the aria-label through props, os even better, allow to include whatever button props we want, like some frameworks does. Material-ui for example (see inputProps in the Input API Docs page.

  <ReactImageGallery fullscreenButtonProps={{ 'aria-label': 'My custom aria-label' }} // .... />

Describe alternatives you've considered
If allowing overwrite whatever prop is not intended for this moment, at last aria-label, maybe fullscreenButtonAriaLabel or fullscreenButtonProps={{ 'aria-label': 'My custom aria-label' }}.

For image thumbnail, would be a new prop inside ReactImageGalleryItem.

{
  // ...
 thumbnailAriaLabel: 'Ir para o slide 1',
  // ...
}

Additional context
Add any other context or screenshots about the feature request here.
N/A.

[xiaolin]

You're able to override the fullscreen button via renderFullscreenButton.

Happy to support thumbnailAriaLabel for thumbnails, feel free to open PR.