added ZabbixAPIEmulator::APIHandlerTriggerGet().

This revision cannot call the added function, because the check of
the auth token fails like
[ERR] <ZabbixAPIEmulator.cc:143> Got exception: <ZabbixAPIEmulator.cc:189> Not found: auth token: 3e24f2a29a97497a33bd39c02f4c06e8
[ERR] <ArmZabbixAPI.cc:333> Failed to get: code: 500: http://localhost:33333/zabbix/api_jsonrpc.php
[ERR] <AsuraThreadBase.cc:164> Got Asura Exception: <ArmZabbixAPI.cc:124> Failed to query triggers.