Opt-in feature: Add database with referrer spam domain names

[Zodiac1978]

Matomo is maintaining a referrer spam list:
https://github.com/matomo-org/referrer-spam-blacklist

Maybe you can use it or add a feature to set up an URL for using it.

[Zodiac1978]

Proof of concept for Statify itself:
https://gist.github.com/Zodiac1978/093244d0b3837cc83c37c2a2a2dc15ea

[stklcode]

Thanks @Zodiac1978 for the suggestion.

I'd imagine a new field like "Include external blacklist" with options Matomo and Custom (which allows specifying a URL - needs documentation, because the list has to match a specific format).

The list obviously must be cached and this shoud be done before the first request (at least in case of live filtering). A daily cron task should do the job here.

The list should be visualized in some way to keep it transparent what will be filtered. I.e. a collapsable panel in the settings page, timestamp of the last update and probably an "update now" button.

The custom filter list stays as is and works entirely in addition to the external list.