This is subtask for ZBXNEXT-3006 to implement front end changes during server side implementation.

Frontend brief implementation plan:

1. API
   • add, get, update, ..
2. add form
   • frontends/php/include/forms.inc.php:811 (getItemFormData())
3. filter by type
   • http://maximt.zabbix.loc/trunk/items.php?filter_hostid=50007
   • getItemFilterForm()
4. edit form
   • same as add, but need check
   • post action frontends/php/items.php:364
5. item validation
   • circular reference
   • dependent item can have master as dependent item (3 level deep restriction)
   • 999 items maximum
6. UI changes on list on items.php
7. import (\CConfigurationImport::processItems())
8. export
9. discovery rules (validation)
10. template sync (reserve ids) \CItem::syncTemplates(), \CTriggerGeneral::createReal()