Add user and hub to websub client subscriptions.

priv/repo/migrations/20170427054757_add_user_and_hub.exs

@@ -0,0 +1,10 @@
+defmodule Pleroma.Repo.Migrations.AddUserAndHub do
+  use Ecto.Migration
+
+  def change do
+    alter table(:websub_client_subscriptions) do
+      add :hub, :string
+      add :user_id, references(:users)
+    end
+  end
+end