Allow to join an open group

Also:

* Refactor interacting with a remote event so that you can interact with
  a remote group as well
* Add a setting for group admins to pick between an open and invite-only
  group
* Fix new groups without posts/todos/resources/events/conversations URL
  set
* Repair local groups that haven't got their
  posts/todos/resources/events/conversations URL set
* Add a scheduled job to refresh remote groups every hour
* Add a user setting to pick when to receive notifications when there's
  new members to approve (will be used when this feature is available)
* Fix pagination for members

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

lib/graphql/schema/event.ex

@@ -17,7 +17,7 @@ defmodule Mobilizon.GraphQL.Schema.EventType do
 
   @desc "An event"
   object :event do
-    interfaces([:action_log_object])
+    interfaces([:action_log_object, :interactable])
     field(:id, :id, description: "Internal ID for this event")
     field(:uuid, :uuid, description: "The Event UUID")
     field(:url, :string, description: "The ActivityPub Event URL")