Add task to migrate data to translation tables

We forgot to do it when we created the translation tables, and so now we
need to make sure we don't overwrite existing translations.

lib/tasks/globalize.rake

@@ -0,0 +1,34 @@
+namespace :globalize do
+  desc "Migrates existing data to translation tables"
+  task migrate_data: :environment do
+    [
+      AdminNotification,
+      Banner,
+      Budget::Investment::Milestone,
+      I18nContent,
+      Legislation::DraftVersion,
+      Legislation::Process,
+      Legislation::Question,
+      Legislation::QuestionOption,
+      Poll,
+      Poll::Question,
+      Poll::Question::Answer,
+      SiteCustomization::Page,
+      Widget::Card
+    ].each do |model_class|
+      Logger.new(STDOUT).info "Migrating #{model_class} data"
+
+      fields = model_class.translated_attribute_names
+
+      model_class.find_each do |record|
+        fields.each do |field|
+          if record.send(:"#{field}_#{I18n.locale}").blank?
+            record.send(:"#{field}_#{I18n.locale}=", record.untranslated_attributes[field.to_s])
+          end
+        end
+
+        record.save!
+      end
+    end
+  end
+end