Starting place for a plugin that adds a webhook

Includes stuff like

 DiscourseEvent.on(:user_created)

and

Plugin::Filter.register(:after_build_web_hook_body) do |

and other basics like

 register_seedfu_fixtures(Rails.root.join("plugins", "discourse-mailchimp-webhook", "db", "fixtures").to_s)

  load File.expand_path('../serializers/mailchimp_serializer.rb', __FILE__)