Anonymous Events should not be sent to logstore

[aspark21]

Should at least provide a site setting to not send the anonymous events to the external logstore.
Currently anonymous parameter is simply discarded

moodle-logstore_caliper/classes/log/store.php

Line 101 in 3a9ee22

unset($evententry['anonymous']);

This should be a criteria to decide wether or not to send this event to the logstore.

We are looking at using Caliper logstore to record engagement with an external system doing the learning analytics crunching. However, the potential for de-anonymising users by non-moodlers is not acceptable as that service will not understand the concept of not using that data