Add unread indicator to conversations (#9009)

db/migrate/20181018205649_add_unread_to_account_conversations.rb

@@ -0,0 +1,23 @@
+require Rails.root.join('lib', 'mastodon', 'migration_helpers')
+
+class AddUnreadToAccountConversations < ActiveRecord::Migration[5.2]
+  include Mastodon::MigrationHelpers
+
+  disable_ddl_transaction!
+
+  def up
+    safety_assured do
+      add_column_with_default(
+        :account_conversations,
+        :unread,
+        :boolean,
+        allow_null: false,
+        default: false
+      )
+    end
+  end
+
+  def down
+    remove_column :account_conversations, :unread, :boolean
+  end
+end