add option to config to enable processing returning unique visitors for week/month/year/range periods (as for normal unique visitors)
implement processing thme in archivePeriod() function in VisitFrequency plugin
The data is now found in the API response, eg:
We do not show it in the UI but more will be done in #539 so please comment there with feedback on how to make the Engagement report better (as we can do a lot to improve reports in general!).