`ContextualMenu`: outside click should be ignored if there is a modal open

When the `closeOnOutsideClick` prop of the `ContextualMenu` is `true`, it should be explicitly checked that there is no modal open before closing the contextual menu on outside click.

This is because, with the current behaviour, a click inside the modal would be captured as outside click for the `ContextualMenu`, causing that to be closed, and since the modal can be a direct child of that `ContextualMenu`, it would end up being removed as well. See the problem more clearly in the following screen capture: