Introduce email settings action hooks
Correct hook name: `woocommerce_email_settings_before`
product by sku
improve get_rating_count() for rating-less reviews

Should close #6839.

According to `woocommerce_enable_review_rating` &
`woocommerce_review_rating_required`, it will do a different DB query,
so that when reviews without ratings are allowed, it will do a query
that counts those comments as reviews.
Adjust total for partially refunded order totals

Closes #6666
Added 'top freebies' to product report.

Closes #5596
Merge pull request #6837 from ragulka/email-settings-action-hooks

Introduce email settings action hooks
Merge pull request #6847 from harrisonde/sku

Look up product by sku
Readme for #6847
Merge pull request #6850 from bryceadams/patch-6839

improve get_rating_count() for rating-less reviews
Revert "Look up product by sku"
Merge pull request #6851 from woothemes/revert-6847-sku

Revert "Look up product by sku"
Created the wc_get_product_id_by_sku() function
[API] Created a route to get products by SKU, closes  #6847
[API] Added error message when try search a product with a invalid SKU
Added numeric sort for attributes. Closes #5978
In the cart, add variation selected data to the permalink.

Closes #6060
Simplify mark_order_status()
Simplify feature_product()
Remove remove_variation and replace with remove_variations