Disable the extention by default. Use a white list instead of a black list

[hansaplasst]

Hi,

I love this plugin.
But for security reasons, blacklisting is NOT the way to go!
The extension should be enabled only on the most common video sites and on sites the user adds. A white list should be used instead of a black list.

Br.
-Hansa

[Veviser]

I've opened a PR for this. I expected Github to attach the PR here but it seems something was wrong with the naming convention. #215