Conversations: Add recipient list to conversation participation.

This enables to address the same group of people every time.

priv/repo/migrations/20190205114625_create_thread_mutes.exs

@@ -6,7 +6,7 @@ defmodule Pleroma.Repo.Migrations.CreateThreadMutes do
       add :user_id, references(:users, type: :uuid, on_delete: :delete_all)
       add :context, :string
     end
-    
+
     create_if_not_exists unique_index(:thread_mutes, [:user_id, :context], name: :unique_index)
   end
 end

priv/repo/migrations/20190801154554_create_conversation_participation_recipient_ships.exs

@@ -0,0 +1,13 @@
+defmodule Pleroma.Repo.Migrations.CreateConversationParticipationRecipientShips do
+  use Ecto.Migration
+
+  def change do
+    create_if_not_exists table(:conversation_participation_recipient_ships) do
+      add(:user_id, references(:users, type: :uuid, on_delete: :delete_all))
+      add(:participation_id, references(:conversation_participations, on_delete: :delete_all))
+    end
+
+    create_if_not_exists index(:conversation_participation_recipient_ships, [:user_id])
+    create_if_not_exists index(:conversation_participation_recipient_ships, [:participation_id])
+  end
+end