Zabbix

.......PS. [ZBXNEXT-1689] updated the server/proxy to work with the new items table structure

* store lastclock,lastns,prevorgvalue values in configuration cache for 'delta' items
* create internal queue check based on configuration cache
* implement queue.get command, which returns statistics of the requested type
* instead of using last/prev values from items table, retrieve those values from history tables.
  After merging valuecache the database calls must be replaced with value cache calls