Documentation: Fix wrong user attribute.
Fix state_filter attribute validation for Depdency objects.

Fixes #6110
Fix exception for Notification objects without checkable object.

Fixes #6111
DB IDO: Update Host/Service status on Acknowledgement Add/Clear.

Refs #6051
DB IDO: Update Host/Service state 'next_check' on NextCheckChanged.

Refs #6051
DB IDO: Update Host/Service state 'is_flapping' on FlappingChanged.

Refs #6051
DB IDO: Update Host/Service state 'last_notification' on NotificationSentToAllUsers.

Refs #6051
DB IDO: Update Host/Service state 'scheduled_downtime_depth' on DowntimeTriggered.

Refs #6051
Merge branch 'feature/db-ido-update-events-6051' into next

Fixes #6051
API thingie (WIP).