Add admin interface to manage instances subscriptions

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

priv/repo/migrations/20191204164224_delete_event_cascade_to_comments.exs

@@ -0,0 +1,19 @@
+defmodule Mobilizon.Storage.Repo.Migrations.DeleteEventCascadeToComments do
+  use Ecto.Migration
+
+  def up do
+    drop_if_exists(constraint(:comments, "comments_event_id_fkey"))
+
+    alter table(:comments) do
+      modify(:event_id, references(:events, on_delete: :delete_all))
+    end
+  end
+
+  def down do
+    drop_if_exists(constraint(:comments, "comments_event_id_fkey"))
+
+    alter table(:comments) do
+      modify(:event_id, references(:events, on_delete: :nothing))
+    end
+  end
+end