update: Show notification on a badly rated site

* Mimic notifications on Firefox and Chrome tos;dr extensions

Signed-off-by: mr.Shu <mr@shu.io>

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Couple of questions:

- right now shows notifications every time the user load a bad rated URL. Should we show this just once per browser session?
- on Firefox clicking on a notification will open the tosdr.org site with the service's rating. Should we do the same here?