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/actors/member.ex

@@ -38,7 +38,6 @@ defmodule Mobilizon.GraphQL.Schema.Actors.MemberType do
     @desc "Join a group"
     field :join_group, :member do
       arg(:group_id, non_null(:id))
-      arg(:actor_id, non_null(:id))
 
       resolve(&Group.join_group/3)
     end