Add data privacy option that are mandatory in some countries

This adds an option for enable IP anonymization. By default it is disabled. For some countries, e.g. Germany, one is forced to set this option if a shop owner does not want to be possibly sued. This is due to national data privacy laws. 

Moreover, an opt-out functionality to be displayed on an imprint is also added. This is also mandatory in some countries, for instance, Germany.

The single commit messages include more detailed information.