Zabbix

.......P.. [ZBX-6630] faster proxy configuration synchronization

This change does not affect how Zabbix server sends configuration updates to a proxy.
It speeds up configuration synchronization on proxy side by reducing a number of
database operations.

Before this change:
   - updates set all fields in records to be modified,
   - special preprocessing for "hostmacro" and "items" table modifies all records in the table.
After this change:
   - updates set only fields whose values differ,
   - special preprocessing for "hostmacro" and "items" table modifies only records and fields
     which are going to be updated and can cause conflict.
   - special preprocessing is added for "hosts_templates" table to avoid conflicts on
     'hostid, templateid' index.