bobatheme: Fix related posts scrollbar; improve SEO tags

- Support opengraph structured properties on image and video
- Add warning if twitter username is missing
- Remove use of style attributes on top level comment section elements
- Add comment explaining why comments.css is not in head
- Add paragraph around comment section "Enable JavaScript" warning
- Remove full-width-hr shortcode
- Adjust margins on related-posts to match rest of body
- Remove unused .full-width-page-list rule
- Fix useless scrollbar on related posts

Author: BBaoVanC