Acknowledgement improvements

- send ack comment to Shinken. Ack comment is user name and comment
- ack all services of an host. From host status array, ack form will
propose to acknowledge all not OK services for the host.
Allow host acknowledgement

Manage host down acknowledgement

To do :
1/ when host is acknowleged, do not count critical services as critical
2/ add button to acknowledge host and all its services in one operation