Zabbix

.......... [DEV-2141] refactored libzbxserver part 1

Merge in ZBX/zabbix from feature/DEV-2141-6.1 to master

* commit '1f7c9d03b00e497dd31af958377065b3e8b3a347':
  .......... [DEV-2141] fixed comments
  .......... [DEV-2141] fixed PR warnings
  .......... [DEV-2141] added static to callback function
  .......... [DEV-2141] fixed PR warnings
  .......... [DEV-2141] refactored libzbxserver
  .......... [DEV-2140] refactored libzbxserver