Added maintenance and host operation. Added check zabbix version for different action in event.acknowledge.

[akitsul]

Added maintenance and host operation with tests.
Added check zabbix version for different action in event.acknowledge:

https://www.zabbix.com/documentation/1.8/api/event/acknowledge
https://www.zabbix.com/documentation/2.0/manual/appendix/api/event/acknowledge
https://www.zabbix.com/documentation/3.4/manual/api/reference/event/acknowledge
https://www.zabbix.com/documentation/4.0/manual/api/reference/event/acknowledge

[kovetskiy]

it's great contribution, one nitpick and we are good

[kovetskiy]

Thanks!