add popup/hover-cards for popular urls, like e.g. twitter

expected result:
a url like https://twitter.com/markusstaab/status/1197832308470034433 when used in e.g. a comment on github should open a card-overlay on mouse-over.
the card-overlay could/should contain the schema.org defined properties like og:title, og:image, og:description etc. like e.g. popular chat systems do (slack, mattermost)

that way people can get a impression on what the actual link will provide/contain without leaving github.com

example how mattermost renders a similar feature:

this feature could be used for several services (as long as the og:* schema is supported by the website) but should not open hover-cards for all links (for security reasons) but just whitelisted domains.

examples I can think of righw now are

• stackoverflow
• medium

Transferred from refined-github/refined-github#2565