make IT Services greater (again?)

[rsturm]

Hi devs,

some ideas to make the "IT-Services" Feature more useful:

1. another status calculation algorithm
   Problem, if more than X childs have a problem (or percentage)
   we use this feature in our Icinga/Nagios-based Monitoring Systems to keep track on the state of Citrix-Farms or Webserverfarms. It is perfectly ok if one or two nodes go offline, but if e.g. more than 20% of the servers are non-functional, the Service fails. Currently we cannot track this in Zabbix IT-Services without another trigger which can be quite complex and we would need to maintain the IT-Service AND the trigger.
   
2. Triggers on IT-Services
   afaik it is not possible to have triggers on IT-Services or their elements. The only alternative is to build huge trigger functions which get hard to maintain. (some of our IT-Services have over 50 Children).
   Additionally, that means, we have to maintain the IT-Service and the trigger at the same time.
   If we could put triggers on IT-Services, life would be a lot easier.