Opengraph

    Add option to get specifically the opengraph image.

    Now we can get the open graph image which is represented by og:image using article.og_image.

    This will help to get the open graph image, it make more sense as, writter of the page specifically choose this
    image to be representative of the webpage.


    Added open graph title, moved open graph image up.

    We have added a option for og:title as og_title.
    Open graph image was inside a check of top_node since og_image is independent of any node, its metadata.
    It was moved out of check,so it will work well.