Minor Description
Currently, when one creates a new notification in Syncope, one is forced to enter a user search condition in the "About" tab that allows to restrict the notifications to specific users. IMO this is not always necessary - it should also be possible to leave the field empty such that the notification is sent for all users.
Allowing the Notification.about field to be empty would also improve performance in this case, as an unnecessary search query to the database can be avoided. This is especially relevant for MySQL, as we observed full table scan behaviour for queries executed by AttributableSearchDAOImpl.matches() (called by NotificationManager) for even very simple search conditions.