Zabbix

..F....... [ZBX-8671] Improve code:
- Use proper isWriteable() instead of get() in permissions check. 
- Remove unnecessary code for request parameters with O_MAND option set. 
- Rewrite code to not write/write to $_REQUEST directly. 
- Replace API_OUTPUT_EXTEND option with specific fields.
- Reorder permissions checks to check groups first.