add a config option to turn off "add validator" links under fields

I don't see a menu item or other config at admin/settings/validation_api for toggling whether or not people have to see the link under every field for adding a validator. People should be able to turn that off after they have configured their validators. The callback is drupal_get_form() with validator_api_admin_settings as the callback parameter that sends back a form processed through system_settings_form().