Add Zabbix input and output plugins

Add Zabbix input and output plugins. 

Zabbix is a monitoring system with agents reporting to the server over regular TCP (although the messages themselves are json). The Zabbix input and output plugins allow zabbix agents that are located behind a firewall or proxy (that may be blocking regular TCP), to communicate with the zabbix server over a HTTP/S channel that is usually open for communication.

Zabbix agents require responses from the zabbix server, therefor I added the ability to return responses via the HTTP input+output plugins.

In addition, I added the ability to specify more than one 'only-type' param, and added a new 'not_type' param that acts as the reverse of 'only_type'.

One last thing I modified was to remove logging of a monitored file event that something changed but no new data exists. This event can happen when 'touching' the file without writing anything to it (such as when using 'touch' on a log file to keep track of a live process)