Changes

tsk97 Adds generation of notifications when an event is cancelled or
modified
Modifies EventEJB so that when an event is cancelled or modified, its
attendees receive a notification. It also sends the notification by
email to those attendees who have previously chosen this feature in
their own profile.
Modifies testing in the Service and Rest layers so they support
Notifications.
Adds new datasets and modifies previous ones to use in the testing
classes.
Modifies the order of deletion in cleanup.sql so that it does not leave
invalid foreign keys.