Introduce comments below events

Also add tomstones

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

priv/repo/migrations/20191114155534_cascade_comment_deletion.exs

@@ -0,0 +1,23 @@
+defmodule Mobilizon.Storage.Repo.Migrations.CascadeCommentDeletion do
+  use Ecto.Migration
+
+  def up do
+    drop(constraint(:comments, "comments_in_reply_to_comment_id_fkey"))
+    drop(constraint(:comments, "comments_origin_comment_id_fkey"))
+
+    alter table(:comments) do
+      modify(:in_reply_to_comment_id, references(:comments, on_delete: :nilify_all))
+      modify(:origin_comment_id, references(:comments, on_delete: :nilify_all))
+    end
+  end
+
+  def down do
+    drop(constraint(:comments, "comments_in_reply_to_comment_id_fkey"))
+    drop(constraint(:comments, "comments_origin_comment_id_fkey"))
+
+    alter table(:comments) do
+      modify(:in_reply_to_comment_id, references(:comments, on_delete: :nothing))
+      modify(:origin_comment_id, references(:comments, on_delete: :nothing))
+    end
+  end
+end