OO-2880: add reference count in the author list of resources, add a filter in the extended to search used and not used resources

OO-2878: add attachment to the info messsages, add the possibility to send the emails only to owners, coaches or participants and not all of them

OO-2947: Option to keep/delete user properties when Shibboleth delivers null and ensure that the mandatory user properties never deleted

OO-2911, OO-2912: enhance the notifications for the task/group task to check the different dates, wording, subscriptions date chooser show the date user for the list notifications and not today

OO-2891: Update the User only if some attribute values have changed. Wording, testing, mMinor improvements in code redability.