user: implement dynamic refresh of profiles (gets rid of need for fix_ap_users task)

priv/repo/migrations/20180919060348_users_add_last_refreshed_at.exs

@@ -0,0 +1,9 @@
+defmodule Pleroma.Repo.Migrations.UsersAddLastRefreshedAt do
+  use Ecto.Migration
+
+  def change do
+    alter table(:users) do
+      add :last_refreshed_at, :naive_datetime
+    end
+  end
+end