GUACAMOLE-220: Add missing definitions for CREATE_USER_GROUP system permission.

guacamole-ext/src/main/java/org/apache/guacamole/net/auth/permission/SystemPermission.java

@@ -37,6 +37,11 @@ public class SystemPermission implements Permission<SystemPermission.Type> {
          */
         CREATE_USER,
 
+        /**
+         * Create user groups.
+         */
+        CREATE_USER_GROUP,
+
         /**
          * Create connections.
          */