#1920 - Download links option supports an array of formats

You have many options for customizing:

`config/initializers/active_admin.rb`

```ruby
ActiveAdmin.setup do |config|
  config.namespace :admin do |admin|
    admin.download_links = false
  end
end
```

`app/admin/admin_users.rb`

```ruby
ActiveAdmin.register AdminUser do
  index download_links: [:xml, :pdf]
end
```

This configuration would hide all download links, except at `/admin/admin_users`, which would show only the XML & PDF format options.