Let pins federate

- save object ids on pin, instead of activity ids
- pins federation
- removed pinned_activities field from the users table
- activityPub endpoint for user pins
- pulling remote users pins

lib/pleroma/web/activity_pub/transmogrifier.ex

@@ -556,6 +556,14 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier do
     end
   end
 
+  def handle_incoming(%{"type" => type} = data, _options) when type in ~w(Add Remove) do
+    with :ok <- ObjectValidator.fetch_actor_and_object(data),
+         %Object{} <- Object.normalize(data["object"], fetch: true),
+         {:ok, activity, _meta} <- Pipeline.common_pipeline(data, local: false) do
+      {:ok, activity}
+    end
+  end
+
   def handle_incoming(
         %{"type" => "Delete"} = data,
         _options
@@ -1000,6 +1008,7 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier do
     with %User{local: false} = user <- User.get_cached_by_ap_id(ap_id),
          {:ok, data} <- ActivityPub.fetch_and_prepare_user_from_ap_id(ap_id),
          {:ok, user} <- update_user(user, data) do
+      {:ok, _pid} = Task.start(fn -> ActivityPub.pinned_fetch_task(user) end)
       TransmogrifierWorker.enqueue("user_upgrade", %{"user_id" => user.id})
       {:ok, user}
     else