OO-3489, OO-3492, OO-3493, OO-3494, OO-3496, OO-3497: infrastructure to export user data, export  portraits, notes, personal folder, calendars, subscriptions, delete calendars after usser deletion

OO-3483: ensure that the email form in member list course element (or group) as at least one recipient

OO-3482: add a check box to confirm the confirmation to delete some user, add more color to the confirmation popup

OO-3477: really remove initial author from repository entry, update course log with the new policy of user properties, springify export manager and co., make logging object annotation based

OO-3477 remove username/email pseudo delete, refactor userdeletemanager to use more the userdatadeletable interface, remove all data from already deleted users