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>

priv/repo/migrations/20201103141811_add_notification_pending_membership_to_settings.exs

@@ -0,0 +1,9 @@
+defmodule Mobilizon.Storage.Repo.Migrations.AddNotificationPendingMembershipToSettings do
+  use Ecto.Migration
+
+  def change do
+    alter table(:user_settings) do
+      add(:notification_pending_membership, :integer, default: 10)
+    end
+  end
+end

priv/repo/migrations/20201105145719_repair_groups_with_missing_ur_ls.exs

@@ -0,0 +1,28 @@
+defmodule Mobilizon.Storage.Repo.Migrations.RepairGroupsWithMissingURLs do
+  use Ecto.Migration
+  alias Mobilizon.Actors.Actor
+  alias Mobilizon.Storage.Repo
+  import Ecto.{Changeset, Query}
+
+  def up do
+    Actor
+    |> where([a], a.type == :Group and is_nil(a.domain))
+    |> Repo.all()
+    |> Enum.each(&fix_group/1)
+  end
+
+  def down do
+    IO.puts("Nothing to revert here, this is a repair step.")
+  end
+
+  defp fix_group(%Actor{type: :Group, domain: nil, url: url} = group) do
+    group
+    |> change(%{})
+    |> put_change(:resources_url, "#{url}/resources")
+    |> put_change(:todos_url, "#{url}/todos")
+    |> put_change(:posts_url, "#{url}/posts")
+    |> put_change(:events_url, "#{url}/events")
+    |> put_change(:discussions_url, "#{url}/discussions")
+    |> Repo.update()
+  end
+end