Add option to show an icon over media elements

[Eloston]

It can be hard to tell what media has been stopped by this extension, and even harder to selectively choose which media to play.
Add an option to show an icon over unknown media types that have been stopped.

• It should be toggleable per-site and globally
• When the icon is clicked, the media should play

[Piter432]

It should be toggleable per-site and globally

Should be also toggleable per-element :)