Add `featured_image` to `opg:image` and `itemprop="image"`

[agektmr]

Currently any update articles don't use featured_image as its actual featuring image. Let's add them as ogp:image and itemprop="image"

[petele]

@agektmr - Do you mean on the listing page or in the article itself?

[agektmr]

@petele In the article itself. This will make tweets and FB posts looking much fancier.