mod_http_admin_api: restructure group-related info in API - Return the members of the group right in the get_group_by_id call. This is an O(1) of extra work. - Remove the groups attribute from get_user_by_name as that is O(n) of work and rarely immediately needed. The replacement for the group membership information in the user is for now to use the group API and iterate; future work may fix that.

Introduction
============

This module checks the IP address of newly registered users against a
DNS block list. If a positive match is found, it gets logged.

Configuration
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  Option              Type     Default
  ------------------- -------- ------------
  registration\_rbl   string   *Required*