Refactor, add beginnings of websub client subscriptions.

priv/repo/migrations/20170426154155_create_websub_client_subscription.exs

@@ -0,0 +1,15 @@
+defmodule Pleroma.Repo.Migrations.CreateWebsubClientSubscription do
+  use Ecto.Migration
+
+  def change do
+    create table(:websub_client_subscriptions) do
+      add :topic, :string
+      add :secret, :string
+      add :valid_until, :naive_datetime
+      add :state, :string
+      add :subscribers, :map
+
+      timestamps()
+    end
+  end
+end