So that classes which extend WC_Abstract_Order can define custom statuses
specifically for their order type and have those used for validation in
WC_Abstract_Order::set_status() instead of only the order statuses defined
by wc_get_order_statuses().
For example, the subscription order type has a number of custom order statuses,
like 'wc-active' and 'wc-expired', which do not apply to orders but are valid
statuses for WC_Subscription objects, which extend WC_Abstract_Order.
* args is not used any more - remove todo
* Added test for attributes
* wc_get_price_excluding_tax usage
* parent usage
* Fix rating counts
* Test fixes
* Cleanup after tests
* Make sure status transition code runs even during API calls, not just in admin.
* Default visibility
* Fix attribute setting in API
* Use get name instead of get title
* variation id usage
* Improved cross sell templates
* variation_data
* Grouped product sync
* Notices
* Sync is not needed in API
* Delete
* Rename interfaces
* Update counts in data store
* No longer needed
* Remove old todos
* Use getters in admin list
* Related and upsells update for CRUD
* Fix notice in gallery
* Variable fixes and todos
* Context
* Price sync
* Revert variation attributes change
* Return parent data in view context
* Defer term counting
* wc_find_matching_product_variation
* Stock manage tweaks
* Stock fixes
* Correct id
* correct id
* Better sync
* Data logic setter fix
* feedback
* Started on variation changes
* Stock functions
* Variation class
* Bulk change ->id to get_id() to fix variation form display
* Missing status
* Fix add to cart
* Start on stored data save
* save variation
* Save_variations
* Variation edit panel
* Save variations code works.
* Remove stored data code and fix save
* Improve legacy class
* wc_bool_to_string
* prepare_set_attributes
* Use wc_get_products
* More feedback fixes
* Feedback fixes
Claudio Sanches
Mike Jolley
Michael Pretty
Claudiu Lodromanean
Boro Sitnikovski
Brent Shepherd
Justin Shreve
Manos Psychogyiopoulos