tools: notifier: Required changes in events data mapping.

The event_audit_log_subscriber_view contains info
about users and events. Since we will need to
provide subscribers from other sources (snmp subscribers
will come from the configuration) we must query the two
separately.

As a result of this: event_audit_log_subscriber_view is dropped,
EventAuditLogSubscriber the entity that represented it is deleted,
and new entities were defined: AuditLogEvent and AuditLogEventSubscriber
AuditLogEventType is no longer an inner class and a new interface,
EventFilter, represents the matching between events and subscribers.
More implementations of this enum will follow.

Mail senders and tests updated to use the new entities.

Change-Id: I3350d1c1caa6d730a3c7916ee0581f1aaa4a582a
Signed-off-by: Mooli Tayer <mtayer@redhat.com>