Create share button on article edit page

[roland-d]

The article edit page needs a button for creating the shared link. This button should also show the just created link. In case the link already exists, only show/hide the share link.

This button is needed for the frontend and backend.

• [x] Create button on the article edit page backend
• [x] Create button on the article edit page frontend
• [x] Create code to act on the button
• [x] The button needs to create the link only if it doesn't exist
• [x] The button needs to toggle a div to show the share link

[nikitadhiman]

instead of toggle div it now shows a clickable message