FEATURE: Support backup uploads/downloads directly to/from S3.

This reverts commit 3c59106bac.

db/migrate/20180916195601_migrate_s3_backup_site_settings.rb

@@ -0,0 +1,33 @@
+class MigrateS3BackupSiteSettings < ActiveRecord::Migration[5.2]
+  def up
+    execute <<~SQL
+      UPDATE site_settings
+      SET name      = 'backup_location',
+          data_type = 7,
+          value     = 's3'
+      WHERE name = 'enable_s3_backups' AND value = 't';
+    SQL
+
+    execute <<~SQL
+      DELETE
+      FROM site_settings
+      WHERE name = 'enable_s3_backups';
+    SQL
+  end
+
+  def down
+    execute <<~SQL
+      UPDATE site_settings
+      SET name      = 'enable_s3_backups',
+          data_type = 5,
+          value     = 't'
+      WHERE name = 'backup_location' AND value = 's3';
+    SQL
+
+    execute <<~SQL
+      DELETE
+      FROM site_settings
+      WHERE name = 'backup_location';
+    SQL
+  end
+end