Ensure we have no duplicate ap ids.

priv/repo/migrations/20170501124823_add_id_contraints_to_activities_and_objects.exs

+defmodule Pleroma.Repo.Migrations.AddIdContraintsToActivitiesAndObjects do
+  use Ecto.Migration
+
+  def change do
+    create index(:objects, ["(data->>\"id\")"], name: :objects_unique_apid_index)
+    create index(:activities, ["(data->>\"id\")"], name: :activities_unique_apid_index)
+  end
+end