Implement statistics

For now, it would be nice to get some information on page visits. In future, when we might expand the website to include a [basic knowledge base](https://github.com/AntennaPod/AntennaPod/issues/1329), it would be nice to get info on that as well. Also, as we might be able to check which features get most attention when we make them 'clickable' (see #4).

Open source options: https://opensource.com/business/14/10/top-3-open-source-alternatives-google-analytics