Notifications: Make notifications save their type.

priv/repo/migrations/20200602094828_add_type_to_notifications.exs

@@ -0,0 +1,9 @@
+defmodule Pleroma.Repo.Migrations.AddTypeToNotifications do
+  use Ecto.Migration
+
+  def change do
+    alter table(:notifications) do
+      add(:type, :string)
+    end
+  end
+end