db: Add United Nations as a demo country

Author: jhf

dbseed/country/country_codes.csv

@@ -235,6 +235,7 @@ Uganda,UG,UGA,800
 Ukraine,UA,UKR,804
 United Arab Emirates (the),AE,ARE,784
 United Kingdom of Great Britain and Northern Ireland (the),GB,GBR,826
+United Nations,UN,UNC,000
 United States Minor Outlying Islands (the),UM,UMI,581
 United States of America (the),US,USA,840
 Uruguay,UY,URY,858