Improve config validation.

Fixes #4391
Update type validators.
config: Count errors and warnings.
config: Add missing "volatile" validator for the Service type.
ido: Add acknowledgements.

refs #4379
ido: Add commenthistory.

refs #4379
ido: Add downtimehistory.

refs #4379
fixes #4710
compatutility: Refactor checkresult output, add notification type mapping.
notifications: Add OnNotificationSentToAllUsers signal.
ido: Add notifications.

refs #4379
Fix crash on missing notification_command.
Refactor CompatComponent class.
Update copyright information.
config: Don't clone host/service attributes.
config: Update validators.
cluster: Don't allow wildcards in endpoint names.
config: Rename Host::hostcheck to Host::check.
config: Rename Host::hostgroups to Host::groups.
config: Rename servicedependencies/hostdependencies.
config: Rename host_name to host.