add `filter:categories.copyPrivilegesFrom`

https://github.com/Schamper/nodebb-plugin-poll/issues/77

src/categories/create.js

@@ -139,9 +139,20 @@ module.exports = function (Categories) {
 	};
 
 	Categories.copyPrivilegesFrom = function (fromCid, toCid, callback) {
-		async.each(privileges.privilegeList, function (privilege, next) {
+		async.waterfall([
-			copyPrivilege(privilege, fromCid, toCid, next);
+			function (next) {
-		}, callback);
+				plugins.fireHook('filter:categories.copyPrivilegesFrom', {
+					privileges: privileges.privilegeList,
+					fromCid: fromCid,
+					toCid: toCid
+				}, next);
+			},
+			function (data, next) {
+				async.each(data.privileges, function (privilege, next) {
+					copyPrivilege(privilege, data.fromCid, data.toCid, next);
+				}, next);
+			}
+		], callback);
 	};
 
 	function copyPrivilege(privilege, fromCid, toCid, callback) {