Implemented container and disablePortal props

[NickCis]

The objetive of this PR is to allow a container (and an optional disablePortal) prop in order to control where the portal element will be rendered.

The implementation was taken from Material UI's Portal component.

This implementation addresses some old issues:

• Portal element defaults to body #145
• Not able to specify parent element of TourPortal #221

I particularly implemented the feature in order to be able to use reactor in a fullscreen element (similarly to #221 ). If a element is displayed in fullscreen (using the browser's requestFullscreen method reactor won't work as the portal will be rendered in document.body. This issue is fixed passing document.fullscreenElement as the container property to the Tour component. You can check the following example:

function useFullscreenElement() {
  const [fullscreenElement, setFullscreenElement] = useState(
    document?.fullscreenElement
  );
  useEffect(() => {
    const handler = () => {
      setFullscreenElement(document.fullscreenElement);
    };

    document.addEventListener("fullscreenchange", handler);

    return () => {
      document.removeEventListener("fullscreenchange", handler);
    };
  }, []);

  return fullscreenElement;
}

function Component() {
  const fullscreenElement = useFullscreenElement();
  return (
    <Tour
      container={fullscreenElement || document.body}
      { ... }
    />
  );
}

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For anyone needing to use this right now it is published on npm under my user's scope: @nickics/reactour.