Advanced event cleaner cronjobs

This plugin provides two task and associated event features:

1. run_anonymize: If the feature anonymize_registrations is enabled on an event, then all registrations will be anonymized if the event is older than 1 year or deleted. The task per default runs on the first of every month. Log entries will be deleted in this case as well.
2. run_cleanup_log: If the feature cleanup_log is set, then clean log entries if the event is older than 1 year. The task per default runs on the first of every month.