Logbook delete/anonymize behavior for organizations

[simonbaese]

The logbook module only handles deletion or anonymization of logs for creative users (see logbook_user_delete).

We first need to decide how the deletion process for an organization should look like, because there is a motivation to keep the related projects. Otherwise, managers or creatives might be confused why their projects are gone. Also, it would affect historical statistics.

After a decision is found the handling of logs without an owner (see Project::getOwner) has to be reworked.