Add admin interface to manage instances subscriptions

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

priv/repo/migrations/20191129091227_add_timestamps_to_followers.exs

@@ -0,0 +1,9 @@
+defmodule Mobilizon.Storage.Repo.Migrations.AddTimestampsToFollowers do
+  use Ecto.Migration
+
+  def change do
+    alter table(:followers) do
+      timestamps()
+    end
+  end
+end