v6.4.2: Add video previews

🐛 Fixes or improvements

• <FullScreenPreview/>: Improved media query style.

📚 Improved documentation.

• Added documentation about new prop on FileItem.
• Added documentation about new component VideoPreview.

🧪 New features

• <FileItem/>: Added onWatch prop. This prop provides an event handler for allowing full screen video previews. It works like onSee prop. It returns as first parameter the file object. If onWatch is present, file is valid and file type is video, FileItem will display the play button.
• <VideoPreview/>: 🎥 Added new componentVideoPreview. This component is quite similar to FullScreenPreview. As the name sugests, this component is meant to be used to show video previews. Supported videos are the default supported videos by a <video/> tag (mp4, ogg, webm). First prop videoSource can be a File object or a URI string representation. Works in the same way as FullScreenPreview, it rcieves a onClose prop and an open prop.
  It also recieves autoplay and controls props like classic html <video/> tag.