Introduce backend for reports

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

priv/repo/migrations/20190718122556_create_admin_action_logs.exs

@@ -0,0 +1,15 @@
+defmodule Mobilizon.Repo.Migrations.CreateAdminActionLogs do
+  use Ecto.Migration
+
+  def change do
+    create table(:admin_action_logs) do
+      add(:action, :string, null: false)
+      add(:target_type, :string, null: false)
+      add(:target_id, :int, null: false)
+      add(:changes, :map)
+      add(:actor_id, references(:actors, on_delete: :nilify_all), null: false)
+
+      timestamps()
+    end
+  end
+end