Adds an initscript for zabbix_server, and related helper files
+ uses a zabbix_server uci conf to enable/disable startup
+ updates the default zabbix_server.conf to work with initscript
+ add a sysctl.d conf to set max-files more appropriate for zabbix_server
Signed-off-by: Daniel F. Dickinson <dfdpublic@wildtechgarden.ca>