generic 'zabbix[host,...]' should replace the limited 'status'

Currently, item 'status' only checks for agent availability and it is only updated when agent's availability changes. One consequence is that any triggers that use this item will remain in the UNKNOWN state until the agent goes down or goes up, which might as well be never. Another consequence is that this item cannot be sensibly graphed. This should be fixed - item 'status' should update like any other item according to the specified interval. Also, while this item should still be supported in 1.8, a more generic 'zabbix[host,...]' should be created that will allow to monitor different parameters of host's availability.