Autocomplete page item cleanup

[tw2113]

1. With get_excluded_post_types() method in class-algolia-settings.php, let's fetch all builtin post types, unset post, page, and attachment and then merge them into the $excluded array. This will prevent having to monitor built in post types going forward.

2. Needs discussion (WooCommerce): remove shop_order and shop_order_refund from autocomplete list. I doubt people want to be able to index orders and refunds on the frontend. Also product_visibility and product_shipping_class from term listing. Those can be modified in get_excluded_taxonomies(). These may be best off via using the available filter and only added if WooCommerce is enabled.