Refactor `PersonStorage` out of `Tracker`

To enable #73 (closed), we should factor out the management of the TrackPersons out of Tracker.

This enables to count each change on the persons.

added enhancement medium refactoring labels

assigned to @d.kilic

mentioned in issue #73 (closed)

created branch 223-refactor-personstorage-out-of-tracker to address this issue

mentioned in merge request !139 (merged)

mentioned in commit aac2b777

closed with merge request !139 (merged)